Friday, January 30, 2009

Interesting Astrophysics: Jan 19 to Jan 30

Interesting astrophysics is back, now with two weeks worth of papers. There look interesting based on the titles and abstracts, but I haven't had time to actually read many of them seriously.

Galaxies and Starbursts

X-ray emission from the extended disks of spiral galaxies
R.A. Owen, R.S. Warwick, arXiv:0901.4263 [ps, pdf, other]
Comments: Accepted for publication in Monthly Notices of the Royal Astronomical Society. 17 pages, 6 figures, 7 tables

I must admit to experiencing a moment of horror and panic when I saw the Owen paper on arXiv and read the abstract - had I been scooped on publishing my own hard-won observations again? Thankfully not, a different set of "normal" galaxies! A nice interesting paper.

GEMINI 3D spectroscopy of BAL + IR + Fe ii QSOs – I. Decoupling the BAL, QSO, starburst, NLR, supergiant bubbles and galactic wind in Mrk 231
S. Lipari, S. F. Sanchez, M. Bergmann, R. Terlevich, B. Garcia-Lorenzo, B. Punsly, E. Mediavilla, Y. Taniguchi, M. Ajiki, W. Zheng, J. Acosta and K. Jahnke, 2009, MNRAS, 392, 1295
Full Text: HTML, PDF (Size: 104115K)

Properties of the Molecular Gas in Starburst Galaxies and AGN
S. Mühle, E.R. Seaquist, C. Henkel, arXiv:0901.3468 [ps, pdf, other]
Comments: 6 pages, 4 figures, proceedings of the 9th European VLBI Network Symposium on "The role of VLBI in the Golden Age for Radio Astronomy and EVN Users Meeting", to appear in Proceedings of Science

Significant emphasis on everyones favorite starburst galaxy: M82.

Galactic Spiral Structure
Charles Francis, Erik Anderson, arXiv:0901.3503 [pdf]
Comments: A high resolution version of this file can be downloaded from this http URL

The Star Formation Histories of the M31 and M33 Spheroids
Thomas M. Brown, arXiv:0901.2577 [ps, pdf, other]
Comments: 7 pages, 2 figures, to appear in the proceedings of "Galaxy Evolution: Emerging Insights and Future Challenges," 11-14 November 2008, Austin, USA

A Wide-field High Resolution HI Mosaic of Messier 31: I. Opaque Atomic Gas and Star Formation Rate Density
Robert Braun, David Thilker, Rene Walterbos, Edvige Corbelli,arXiv:0901.4154 [ps, pdf, other]
Comments: Accepted for publication in ApJ, 34 pages, 20 figures

A Multi-Wavelength Infrared Study of NGC 891
C. Whaley, J. Irwin, S. Madden, F. Galliano, G. Bendo, arXiv:0901.4351 [ps, pdf, other]
Comments: 24 pages, 17 figures, 7 tables, accepted for publication in MNRAS

Distance to NGC 0247
Barry F. Madore, Wendy L. Freedman, J. Catanzarite, Mauricio Navarrete, arXiv:0901.3097 [ps, pdf, other]
Comments: Accepted ApJ Nov 2008: 51 pages, 19 figures, 16 tables

A Search for Radio Supernova Remnants in Four Irregular Galaxies
Laura Chomiuk, Eric Wilcots, arXiv:0901.2919 [ps, pdf, other]
Comments: Accepted by AJ. 17 pages, 9 figures. 23 additional figures will be available in the online version of the Astronomical Journal

The rotation curves shapes of late-type dwarf galaxies
R.A. Swaters, R. Sancisi, T.S. van Albada, J.M. van der Hulst, arXiv:0901.4222 [ps, pdf, other]
Comments: 22 pages, 2009 A&A 493, 871
Journal-ref: A&A, 493, (2009) 871

Diverging UV and Halpha fluxes of star forming galaxies predicted by the IGIMF theory
J. Pflamm-Altenburg, C. Weidner, P. Kroupa, arXiv:0901.4335 [ps, pdf, other]
Comments: accepted by MNRAS

Ram pressure stripping of the multiphase ISM in the Virgo cluster spiral galaxy NGC 4438
B. Vollmer, M. Soida, A. Chung, L. Chemin, J. Braine, A. Boselli, R.Beck, arXiv:0901.2770 [ps, pdf, other]
Comments: 8 pages, 6 figures, A&A, accepted for publication

Numerical Simulations of Hot Halo Gas in Galaxy Mergers
Manodeep Sinha, Kelly Holley-Bockelmann, arXiv:0901.3782 [ps, pdf, other]
Comments: Submitted to MNRAS. Paper with high-resolution images and associated movies available at this http URL

Correlations Between Supermassive Black Holes, Velocity Dispersions, and Mass Deficits in Elliptical Galaxies with Cores
John Kormendy, Ralf Bender, arXiv:0901.3778 [ps, pdf, other]
Comments: 4 pages, 4 figures, 1 table; requires emulateapj.sty
Journal-ref: 2009 ApJ 691 L142-L146

This Kormendy would be more interesting if it weren't so damned short. I suppose we'll have to wait for the real paper to come out to really assess this. This smacks of the "publish two for the price of one and get publication date priority" style of gaming the publish-or-perish system.

Different types of ultraluminous X-ray sources in NGC 4631
Authors: Roberto Soria, Kajal Ghosh, arXiv:0901.4302 [ps, pdf, other]
Comments: 12 pages, accepted by ApJ

Numerical Astrophysics and Hydrodynamics

iVINE – Ionization in the parallel tree/sph code VINE: first results on the observed age-spread around O-stars
M. Gritschneder, T. Naab, A. Burkert, S. Walch, F. Heitsch and M. Wetzstein, 2009, MNRAS, 393, 21
Full Text: HTML, PDF (Size: 2038K)

Spectral Analysis in the Virtual Observatory
Thomas Rauch, Iliya Nickelt, arXiv:0901.4202 [ps, pdf, other]
Comments: 3 pages


Missing Halo Baryons and Galactic Outflows
Romeel Davé, arXiv:0901.3149 [ps, pdf, other]
Comments: 7 pages, to appear in proc. "Galaxy Evolution: Emerging Insights and Future Challenges", ASP (uses asp2006.sty)

The Effects of Gas on Morphological Transformation in Mergers: Implications for Bulge and Disk Demographics
Philip F. Hopkins, Rachel S. Somerville, Thomas J. Cox, Lars Hernquist, Shardha Jogee, Dusan Keres, Chung-Pei Ma, Brant Robertson, Kyle Stewart, arXiv:0901.4111 [ps, pdf, other]
Comments: 19 pages, 13 figures, submitted to MNRAS

Apparent discordant redshift QSO-galaxy associations
Martin Lopez-Corredoira, arXiv:0901.4534 [ps, pdf, other]
Comments: invited talk, to be published in the proceedings of the conference "Evolution of Cosmic Objects through their Physical Activity (V. Ambartsumian 100th anniversary)", held at Byurakan Observatory (Armenia), on September 15th-18th, 2008. Eds. H. A. Harutyunian, H. Y. Terzian. Armenian Academy of Sciences

All I can say is that in the one case where I have really examined this sort of thing seriously (NGC 3628, which is mentioned in this article although not elaborated upon), both the qualitative claims of physical association between QSO and the NGC 3628 superwind, and the quantitative claims of the QSO's presence in the field of view being statistically unlikely simply failed to hold up under examination. See Strickland et al, 2004a, ApJS, 151, 193 (footnote 11).

Astrophysical Plasmas

Giant cavities, cooling and metallicity substructure in Abell 2204
J. S. Sanders, A. C. Fabian and G. B. Taylor, 2009, MNRAS, 393, 71
Full Text: HTML, PDF (Size: 17147K)

The effect of photoionization on the cooling rates of enriched, astrophysical plasmas
Robert P. C. Wiersma, Joop Schaye and Britton D. Smith, 2009, MNRAS, 393, 99
Full Text: HTML, PDF (Size: 389K)

Stars, Supernovae, Star Clusters, Planets etc.

Chemical Yields from Supernovae and Hypernovae
Ken'ichi Nomoto, Shinya Wanajo, Yasuomi Kamiya, Nozomu Tominaga, Hideyuki Umeda, arXiv:0901.4536 [ps, pdf, other]
Comments: 13 pages, 10 figures. To appear in the Proceedings of IAU Symposium 254 "The Galaxy Disk in Cosmological Context" (2008), eds. J. Andersen, J. Bland-Hawthorn, and B. Nordstrom (Cambridge University Press)

Title: Tangential Motions and Spectroscopy within NGC 6720, the Ring Nebula
C. R. O'Dell, W. J. Henney, F. Sabbadin, arXiv:0901.3185 [pdf, other]
Comments: Astronomical Journal, in press

Whilst this Planet Has Gone Cycling On: What Role for Periodic Astronomical Phenomena in Large Scale Patterns in the History of Life?
B.S. Lieberman, A.L. Melott, arXiv:0901.3173 [pdf]
Comments: 39 pages, 5 figures, to be published in the Biosphere volume of the International Year of Planet Earth Series, J. Talent, Ed

Tuesday, January 27, 2009

The Future of Nuclear Power

SciAm has an interesting web special feature containing a large number of articles regarding nuclear power: Nuclear power as a means to reduce CO emission; new reactor designs; Uranium supplies; the issues and problems associated reprocessing nuclear fuel.

All very interesting from a physics point of view, although with the mix of pros and cons presented in the different articles its hard to get a sense of whether we'll actually end up with a new set of (advanced?) reactors being built.

Friday, January 16, 2009

Interesting Astrophysics: Jan 12 - Jan 16

Another week, and another dose of preprints (and maybe some actual refereed papers too) that strike my fancy. There are a decent number of papers on or related to starbursts, and even a few papers that can be loosely considered as somewhat related to galactic winds as well, both of which are nice.

"Interesting Astrophysics" will return in two weeks time.

Galaxies and Starbursts

Magnetic structure of our Galaxy: A review of observations
J. L. Han, arXiv:0901.1165 [ps, pdf, other]
Comments: 10+1 pages. Invited Review for IAU Symp.259: Cosmic Magnetic Fields: From Planets, to Stars and Galaxies (Tenerife, Spain. Nov.3-7, 2009). K.G. Strassmeier, A.G. Kosovichev & J.E. Beckman (eds.)

Yes, I know this is very similar to the Han conference proceedings (arXiv:0901.0040) in last week's Interesting Astrophysics.

Cosmic-ray driven dynamo in the medium of irregular galaxy
Hubert Siejkowski, Marian Soida, Katarzyna Otmianowska-Mazur, Michał Hanasz, Dominik Bomans, arXiv:0901.1566 [pdf, other]
Comments: 2 pages, 2 figures, To be published in "Cosmic Magnetic Fields: From Planets, to Stars and Galaxies", K.G. Strassmeier, A.G. Kosovichev & J.E. Beckman, eds., Proc. IAU Symp. 259, CUP

Cluster magnetic fields from galactic outflows
J. Donnert, K. Dolag, H. Lesch and E. Müller, 2008, MNRAS, 392, 1008
Full Text: HTML, PDF (Size: 55539K)

Modelling Starbursts in HII Galaxies: What do we need to fit the observations?
M. L. Martin-Manjon, M. Molla, A. I. Diaz, R. Terlevich, arXiv:0901.1186 [ps, pdf, other
Comments: 6 pages, 5 figures, proceedings to "Star-forming Dwarf Galaxies:
Ariadne's Thread in the Cosmic Labyrinth", Crete, 2008

The role of E+A and post-starburst galaxies I. Models and model results
Marie Aylin Falkenberg, Uta Fritze, arXiv:0901.1665 [ps, pdf, other]
Comments: accepted for publication in MNRAS; 14 pages, 21 figures;

Role of galactic gaseous halos in recycling enriched winds from bulges to disks: A new bulge-disk chemical connection
K. Bekki, T. Tsujimoto, M. Chiba, arXiv:0901.1355 [ps, pdf, other]
Comments: 13 pages, 4 figures (1 color), accepted by ApJL

I must take time out to read this at some point.

Radio Recombination Lines toward the Galactic Center Lobe
C. J. Law, D. Backer, F. Yusef-Zadeh, R. Maddalena, arXiv:0901.1480 [ps, pdf, other]
Comments: Accepted to ApJ. 17 pages, 9 figures, emulateapj style

An Ultra Compact Dwarf around the Sombrero galaxy (M104): the Nearest Massive UCD
George K. T. Hau, Lee R. Spitler, Duncan A. Forbes, Robert N. Proctor, Jay Strader, J. Trevor Mendel, Jean P. Brodie, William E. Harris, arXiv:0901.1693 [pdf, other]
Comments: 5 pages, MNRAS Letters accepted

AGN and Black Holes

AGN and starburst in bright Seyfert galaxies: from IR photometry to IR spectroscopy
Luigi Spinoglio, Silvia Tommasin, Matthew A. Malkan, arXiv:0901.1212 [ps, pdf, other]
Comments: Invited talk at the conference "A Long Walk Through Astronomy: a celebration of the scientific contributions of Luis Carrasco on his 60th Birthday", October 15-17, 2008, Huatulco, Oaxaca (Mexico). Editors: E. Recillas, L. Aguilar, A. Luna, J.R. Valdes. To be published in the RevMexAA (Serie de Conferencias)

Do Moderate-Luminosity AGN Suppress Star Formation?
Kevin Schawinski, Shanil Virani, Brooke Simmons, C. Megan Urry, Ezequiel Treister, Sugata Kaviraj, Bronika Kushkuley, arXiv:0901.1663 [ps, pdf, other]
Comments: Accepted for publication in ApJ Letters. 7 pages, 4 figures

Kinematic and Excitation Structure of the NGC 1068 Narrow-Line Region
Shinobu Ozaki, arXiv:0901.1704 [ps, pdf, other]
Comments: 18 pages, 17 figures. Accepted for publication in PASJ

This has some nice-looking work on radiation-driven clouds, which I really should spend some time reading more carefully.

Numerical Astrophysics and Hydrodynamics

Gas Stripping in Simulated Galaxies with a Multiphase ISM
Stephanie Tonnesen, Greg L. Bryan, arXiv:0901.2115 [ps, pdf, other]
Comments: 17 pages, 12 figures, accepted in ApJ

3D numerical model of the Omega Nebula (M17): simulated thermal X-ray emission
J. Reyes-Iturbide, P. F. Velazquez, M. Rosado, A. Rodriguez-Gonzalez, R. F. Gonzalez, A. Esquivel, arXiv:0901.2142 [ps, pdf, other]
Comments: 8 pages, 6 figures, accepted for publication in MNRAS

Stars, Star Clusters and Planets

Spitzer View of Young Massive Stars in the LMC HII Complex N44
C.-H. Rosie Chen, You-Hua Chu, Robert A. Gruendl, Karl D. Gordon, Fabian Heitsch, <arXiv:0901.1328 [ps, pdf, other]
Comments: 63 pages, 15 figures, accepted for publication for ApJ; some figures
in jpeg format to meet the size limit; preprint with high resolution images
can be found at this http URL

Highly Accelerated Diamagnetic Plasmoids: A New X-ray Production Mechanism for OB Stellar Winds
Wayne L. Waldron, Joseph P. Cassinelli, arXiv:0901.1405 [ps, pdf, other]
Comments: Accepted for publication in ApJ Letters, 4 pages, 4 figures (color), 1 table

Thursday, January 15, 2009

Methane from Mars

Mars + Methane = Life? Big NASA press event today. Read about it at the Loom (Carl Zimmer's blog).

[Image of Martian releasing methane taken from NASA Mars Reconnaissance Orbiter website. Just kidding, it is actually a cool War of the Worlds poster available here.]

Press releases from last week's AAS meeting in Long Beach, CA.

A variety of astronomy highlights and press releases from last week's AAS meeting in Long Beach, CA made it into the popular science media, in particular, but also the BBC and the NYT (unless otherwise noted, the links are to a article). I chosen to cover four stories from the AAS that made it into the popular science media.

Unfortunately the meeting website and the AAS don't seem to link to or archive the these press releases. In some cases all that is available is the pop science write-up, which may or may not accurately reflect what the scientists involved wanted to present. It used to be the case that press releases only happened on the publication of a full peer reviewed Journal article, but this is the AAS where you typically announce work-in-progress and so full papers may still be in the works.

(1.) "Mystery Roar from Faraway Space" by Andrea Thompson discusses an excess component in the Extragalactic Radio background (in the 3 to 90 GHz band) discovered in data from the ARCADE 2 balloon experiment. Emission in this band is a combination of a signal due to the Cosmic Microwave Background (the remainder radiation from the Big Bang), a foreground signal from our own Galaxy, and the integrated emission from extra-galactic sources (in particular galaxies). The claim is that after accounting for known sources and the expected contribution from galaxies there is a residual component to the radio background with a spectral index of -2.56 +/- 0.04 (the actual submitted paper is Seiffert et al, arXiv:0901.0559).

The actual paper spends quite a bit of time trying to demonstrate that they have good "evidence for isotropic radio emission... beyond what can be explained Galactic emission and the unresolved emission from the known population of discrete sources" [i.e. galaxies], but the paper doesn't really speculate as to what the source of this component is. The argument that this excess can not be due to galaxies is a pretty good one. Astronomers have a good idea of how much radio emission to expect from all the galaxies in the Universe because galaxies obey the relatively tight radio/FIR correlation (the massive stars whose explosions ultimate create the cosmic ray electrons responsible for galactic radio emission also heat dust to IR-emitting temperatures), and if galaxies were responsible for the excess radio emission then we'd expect a higher IR background than we see.

Thompson's write up (nicely) doesn't go beyond the submitted paper: 'For now, the origin of the signal remains a mystery. "We really don't know what it is," said team member Michael Seiffert of NASA's Jet Propulsion Laboratory in Pasadena, Calif.'

This story is also covered by Dennis Overbye at the NYT on January 7th ("Theory Ties Radio Signal to Universe's First Stars"). This article goes rather further than the actual submitted paper, spending quite a bit of time discussing Alan Kogut's (NASA/GSFC) admittedly "wildly speculative" suggestion that the excess emission originates from black holes formed by the collapse of the first stars to form in the Universe (Population III stars).

(2.) "Explosions Starve Black Holes" by Andrea Thompson discusses results presented by Daniel Wang (Hi Daniel), but I'm confused as what new result its reporting, or whether its theory or observational data despite the subject matter (galaxies, X-rays, supernova-heated hot gas) being very close to stuff I do. I could not find an actual press release on the UMass or JPL web sites, nor a paper on arXiv. The the idea that supernova heating in prevents/explains the lack of accumulation of large masses of cool/warm interstellar medium (by cool or warm I mean gas with temperatures less a few million degrees) from recycled gas from evolved stars in old stellar populations (ellipticals, bulges) is not new, dating back to the 1960's. That AGN will accrete less in a hot low density ISM is also
self-evident. Nevertheless, despite my lack of understanding regarding the news item I've included it in this list because I know Daniel and hot gas in galaxies also deserves more media attention.

(3.) "Surprise! Milky Way Much More Massive" by Andrea Thompson discusses new Very Long Baseline Array (VLBA) radio observations of Masers that indicate that the rotational velocity (and hence mass) of our Milky Way galaxy is higher than previously thought (by approximately 15% above the old standard of rotation speed 220 km/s, and ~50% higher in mass). This is also covered by Kenneth Chang at the NYT ("Data Uncover Bigger Galaxy in Cosmos, and It’s Ours" ), at the BBC ("Milky Way 'bigger than thought'" ), and NRAO's full press release ("Milky Way a Swifter Spinner, More Massive, New Measurements Show") is here. The image shown at the start of this post is taken from the NRAO press release, and shows an artist's impression of the Milky Way (as viewed from above) along with our location (red circle) and the location of the maser sites (green, blue circle?).

The basic method is to exploit the amazing spatial resolution given by very long-baseline radio interferometry to measure trigonometric parallaxes (and hence the distance) to methanol masers (simpler wikipedia article on masers here) in massive star forming regions in our galaxy. This is a direct distance measurement, and hence doesn't rely on multiple error-prone steps in the Cosmological Distance Ladder. From the doppler shifts of the radio emission one also has the line-of-sight velocity of the source with respect to us. Thus you have size and velocity measurements, although how you go beyond that to get a rotation model for the Galaxy isn't immediately obvious to me (remedial reading of Galactic Dynamics or Galactic Astronomy is hereby self-assigned).

Unfortunately this is another result that doesn't appear (AFAIK) to be associated with a publically available recent paper (no obvious arXiv preprint, no published paper that I can find, no paper mentioned in the NRAO press release). Papers on distances to individual star forming by members of this team are on arXiv, but don't mention changing the previously accepted value of the Milky Way's rotational velocity (Brunthaler et al, arXiv:0811.0713; Rygl et al, arXiv:0812.0905 ).

However, I did remember this issue was mentioned in Shattow and Loeb's paper on the LMC 's orbit (2008, MNRAS, 392, L21 ), and sure enough they say: "Also, within the past five years, the circular velocity of the MW and the distance between the Sun and the Galactic Centre have been updated by Reid & Brunthaler (2004; hereafter RB04) and Gillensen, Genzel & Eisenhouer (private communication; hereafter GGE08), respectively. These increased the likely circular velocity of the MW from the IAU standard of Vcirc = 220 to 251 ± 15 km s−1. A value of 220 km s−1 now corresponds to a reduction of the best-fitting value by two standard deviations (and equivalent to moving the Sun a total of 1 kpc closer to the centre of the Galaxy). Uemura et al. (2000) used parallax measurements from Hipparcos and SKYMAP to obtain a similar value of Vcirc = 255 ± 8 km s−1."

Here are the links to the Reid and Brunthaler (2004) and Uemura et al (2000) papers:
1. "The Proper Motion of Sagittarius A*. II. The Mass of Sagittarius A*," Reid and Brunthaler, 2004, ApJ, 616, 872. (Note that this paper gives theta_0 = 236 +/- 15 km/s, with the error dominated by the 0.5 kpc uncertainty in R_0.)
2. "Galactic Rotation Derived from OB Stars Using Hipparcos Proper Motions and Radial Velocities," Uemura et al, 2000, PASJ, 52, 143. They obtained v_theta = 255 +/- 8 km/s.

So although this result might actually be a few years old and not "hot of the presses" new, it certainly was news to me and is a nice example of how we continue to reassess the nature of our own Galaxy.

(4.) "Black Holes Preceded Galaxies, Discovery Suggests" by Andrea Thompson. This is a story that got a lot of press and blog attention, much of which typically fails to include the important qualifier "suggests" that Thompson includes in her title (good for you Andrea!). The BBC article is another offender ("Black holes 'preceded galaxies'" ). Interestingly this story was not touched by the NYT. The core scientific result is an impressive technical achievement and is scientifically interesting and important. Unfortunately the press releases go beyond what the data is saying.

One of the most striking differences between our current view of the supermassive black holes (SMBHs) that power AGN and the galaxies within which they reside, and what we knew say 15 years ago when I was in grad school is that we now that galaxy growth and black hole growth are linked some how. In the local z=0 (here and now) Universe, 13.7 billion years after the Big Bang, those galaxies that have SMBHs (not all do, many lower mass galaxies appear not to have SMBHs at all) have SMBHs that weigh typically about 0.1% of the galaxy mass (there are of course arguments over whether the fundamental relationship is BH mass to galaxy stellar (baryonic) mass or to just the mass of the galaxies Bulge stellar population, or the mass of the entire halo including the Dark Matter, but you get the picture).

This strongly suggests that galaxy growth (star formation from gas) and black hole growth (accretion of gas) are somehow linked and possibly regulate one another. This was a shocking result. Some astronomers now speculate that AGN control or limit star formation on galactic scales, other speculate that star formation regulates/limits accretion onto SMBHs, and other suggest that the size of the galaxy's dark matter halo ultimately controls both star formation and the accretion onto the SMBH. All very different and much more complex and almost ecological compared to the view back in the early 1990's where theories of galaxy formation and AGN growth were essentially separate, their evolution disconnected from one another.

The Carilli et al press release is basically about measuring the ratio of the mass of the SMBH to the galaxy in four high redshift AGN. Do these much younger galaxies, only a billion or two years old, have the same ratio as the older galaxies now do? That is, were the BH and stellar growth rates constrained by whatever process in the same way over the entire history of the Universe? This is a fascinating question, and the answer appears to be no. In Carilli et al's four high-z AGN the SMBH appears to be proportionally much more massive than in local galaxies. Or alternatively the galaxies (mainly stars) are less massive.

Whichever way you put it, the black holes in these particular galaxies in early Universe appear to have grown faster relative to the galaxy than the long term average we now see imprinted in galaxies at z=0 .
Qualitatively this result is not entirely unexpected (read the nice introduction to Haiman, 2006, New Astronomy Reviews, 50, 672 ) but actually managing to get quantitative measurements is a great piece of science nonetheless. Good job (so far) guys!

Its at this point things start to go wrong, IMHO. These galaxies they're observing are young, but not primeval - and they still have most of their mass in stars. The period is still ~1.5 billion years after the Big Bang and about a billion years after the first stars and galaxies began to form.

Yet the result is extrapolated to much earlier times and to discuss what came first: Black Holes or stars? “Black holes came first and somehow—we don’t know how—grew the galaxy around them,” Carilli says [ ]. "The implication [emphasis mine] is that the black holes started growing first." Fabian Walter is quoted as saying [BBC article ]. But the data itself doesn't tell you what happed. Its at least equally plausible that the first stars came before the black holes, but then the black hole growth rate briefly surged.

The data says that the SMBHs are proportionally more massive with respect to the galaxy mass at high redshift than at low redshift. A reasonable extrapolation of this is to say that the black holes grew proportionally faster than the galaxies, averaged over the entire 1.5 billion year period after the Big Bang. But its a big leap to say the Black Holes formed first. If the stellar/galactic and Black Hole growth rates are no longer inextricably coupled then we have less, not more, of a handle on the age!

Yet from reading the popular press Joe Public would get the incorrect impression that science has solved the problem and worked out that Black Holes came before galaxies. I only highlight this particular case because this seems me to be a typical problem with popularizing science and with press releases: The qualifying statements get stripped out, and the possible-but-speculative implications of a result end up getting higher billing than the real science itself.

As a side note, the SciAm article on this has an update mentioning that even the basic science result may not be robust but instead be a statistical artifact. No doubt this work will spur other groups to perform similar studies, so time will tell whether the results of relatively larger SMBH to galaxy mass in the early Universe holds true. Nevertheless, very interesting work despite the annoying PR spin.

SciAm article on cost overruns at NASA

SciAm online has a short article by George Musser on cost overruns in NASA science projects and their various causes. All pretty standard stuff. It does end with the following sad-but-true aside:

Some finances, though, are beyond NASA’s control. Five years ago President George W. Bush ordered NASA to replace the shuttle but failed to pay the transition costs, forcing NASA to make internal cuts, such as eliminating technology development and delaying projects that were ready to go, which ultimately raised costs. If those who foot the bill expect NASA to make the best use of their money, then it would help if they, too, set expectations in line with resources.

Tuesday, January 13, 2009

Myths about Peer Review

Michael Nielsen has an interesting article discussing three myths about scientific peer review.

I certainly wasn't aware how little peer review was used until recently. For example, perhaps only one of Einstein's 300 papers was subject to what we modern scientists consider as peer review, and Einstein was far from pleased at the (correct) negative report he obtained.

I'm less than convinced by Nielsen's claim (Myth 2) that peer review is not reliable. Its not perfect, but just because its not perfect does not mean that it doesn't serve some useful function at all. All practicing scientists certainly know the system has a large random component. With respect to papers destined for Journals I'd say on peer review has improved all my papers (although often in very minor ways) and that my reviews of other's papers have improved them. Some of the stuff in a Referee's report turns out to be a waste of time, other parts may be good suggestions or advice, and other parts total misreadings or misunderstandings of the paper (in which case you know other readers will probably also misunderstand it too, so you'd better explain yourself better).

In the two cases where I have rejected a paper in the 14 years of my scientific career (including my time as a PhD student) both cases had demonstrable fatal flaws. Both of those were theory papers with mistakes that a non-expert almost certainly would not have identified themselves, and thus letting them enter the literature would have been detrimental. Bad observational papers are harder to reject as the data may be ultimately useful even if the Author's analysis is sub-par or their interpretation is merely crazy speculation.

Peer-review, as applied to grant or observing time, certainly has a larger random component that reviewing papers, but that is understandable given the broader range of science you'd encounter on a peer review committee (i.e. subjects further from your own specialized area of expertise), and the large number of proposals the committee has to read, rate and debate in the short amount of time allocated. A committee may like a proposal one year that another committee didn't like a previous year. There is a large random component in the absolute ranking of proposals, but generally people can come to agreements on what are the best and worst proposals. At that imperfect level peer review works.

Nielsen's Myth 3 is correct. Just because a paper passes peer review does not mean it is correct!

But I do think peer review is a necessary component of modern science, even if (as Nielsen argues) science functioned acceptably without widespread peer review in the 19th and early 20th centuries. Modern science is vastly larger and more complex in scope and depth that it was even 50 years ago. The degree of specialization is such that even the smartest and most widely-read scientists can not fully judge papers outside their own narrow range of expertise themselves. Peer review is an imperfect filter, but without it there would be even more wrong science out there. There is no way that increasing the amount of flawed, bad or fundamental wrong papers can be beneficial to science, can there?

Ultimately peer review requires that you have informed, qualified, peers (I suppose they're not technically peers if they aren't qualified). If science becomes so specialized that no-one else understands anyone else's work then peer review will fail. Similarly "peer" review by unqualified reviewers doesn't work (e.g. the slashdot comment rating system - as the number of readers increased and their average technical knowledge decreased the system devolved in to pure uninformed opinion. Eventually the signal-to-noise ratio decreased so far that I personally consider slashdot unreadable). Reviewers have to know something to make useful reviews!

Its also worth remembering that astronomy/astrophysics journals have relatively low rejection rates compared to other sciences. If I were in a field where my papers suffered a 50% chance of being rejected I might have a less positive view of peer review!

Friday, January 09, 2009

Interesting astrophysics: Jan 05 - Jan 09

With the new year finally underway and all the annoying holidays over there is more in the way of interesting peer-reviewed and preprint astrophysics available this week. To make my comments more clearly separable from the preprints/papers I'm going to switch to using italic for any personal comments below the dividing line below.

There has also been some interesting galaxy and galaxy formation stuff coming out the this week's American Astronomical Society meeting in Long Beach (I didn't go, as I consider AAS meetings overly expensive drains of grant money given that you get less detailed science out of them) at least in press release form (and with press release hype too, in one case). If time permits I'll cover those separately.

Galaxies and Starbursts

New knowledge of the Galactic magnetic fields
J.L. Han, arXiv:0901.0040 [ps, pdf, other]
Comments: 8 pages, 4 figures. Invited Talk at XIV International Symposium on Very High Energy Cosmic Ray Interactions, WeiHai, China 15-22 Aug 2006
Journal-ref: Nuclear Physics B Proc. Suppl 175, 62 (2008)

Interplay of CR-driven galactic wind, magnetic field, and galactic dynamo in spiral galaxies
Marita Krause, arXiv:0901.0845 [ps, pdf, other]
Comments: 2 pages. To be published in "Cosmic Magnetic Fields: From Planets, to Stars and Galaxies", K.G. Strassmeier, A.G. Kosovichev & J.E. Beckman, eds., Proc. IAU Symp. 259, CUP

This seems to be the most interesting part of the Krause preprint, at least with respect to galactic winds:
"For NGC 253 Heesen et al. (this volume) argued that the synchrotron lifetime (which is / B_{t}^{−2}) mainly determines the vertical scale height of the synchrotron emission and estimated the cosmic ray bulk velocity to 300±30 km/s. As this is similar to the escape velocity, it shows the presence of a galactic wind in this galaxy. The fact that we observe similar averaged scaleheights at lambda = 6 cm for the four galaxies mentioned above imply that the galactic wind velocity is proportional to B^{+2}_{t}, and hence proportional to SFR^{0.7±0.3}."
Their are a number of differences between their interpretation and non-radio-based studies of galactic winds. Firstly, their argument is that the scale height of the radio emission is related the lifetime (and hence velocity) of the synchrotron emitting CR population, and implicitly that v_{CR} is equivalent to the wind velocity. This is very different to our interpretation of what sets the apparent 1 to 4 kpc scale height of the X-ray-emitting halos in starbursts, which was that it was the scale-height of the pre-existing halo made visible through the collision between the outflowing wind and the halo. Secondly, optically-measured velocities (using the NaD doublet in absorption) in superwinds (again, NOT NECESSARILY THE SAME AS THE TRUE WIND VELOCITY), appear to show v_{opt} proportional to SFR^{1/3} at low and moderate SFR before peaking at or below 1000 km/s at high SFR (ULIRG class galaxies), see e.g. Martin (2005). Admittedly these optical results have a lot of scatter and uncertainty, and the trends are partially driven by low number statistics at the low SFR end, but we did find the same general trend using UV-absorption lines in Grimes et al (in press). Anyway, their work is interesting, even if I doubt buy the interpretation.

Imaging the Circumnuclear Region of NGC 1365 with Chandra
Junfeng Wang, G. Fabbiano, M. Elvis, G. Risaliti, J. M. Mazzarella, J. H. Howell, S. Lord, arXiv:0901.0297 [ps, pdf, other]
Comments: Accepted for publication in The Astrophysical Journal (April 2009). 50 pages, 13 figures, 6 tables

Star Formation Around Supergiant Shells in the LMC
Laura G. Book, You-Hua Chu, Robert A. Gruendl, Yasuo Fukui, arXiv:0901.0400 [ps, pdf, other]
Comments: 12 pages, 4 figures, accepted for publication in the Astronomical Journal, improved image quality of figures

Ionization of Infalling Gas
L. M. Haffner, A. K. Duncan, S. M. Hoffman, G. J. Madsen, A. S. Hill, R. J. Reynolds, arXiv:0901.0940 [ps, pdf, other]
Comments: 4 pages, 2 figures; to appear in proceedings of "The Role of Disk-Halo Interaction in Galaxy Evolution: Outflow vs Infall?" held in Espinho, Portugal during 2008 August

The warm ionized medium in spiral galaxies
L. M. Haffner, R.-J. Dettmar, J. E. Beckman, K. Wood, J. D. Slavin, C. Giammanco, G. J. Madsen, A. Zurita, R. J. Reynolds, arXiv:0901.0941 [pdf, other]
Comments: 29 pages, 19 figures; accepted by Reviews of Modern Physics

The mass-metallicity gradient relation of early-type galaxies
Max Spolaor, Robert N. Proctor, Duncan A. Forbes, Warrick J. Couch, arXiv:0901.0548 [ps, pdf, other]
Comments: 5 pageg, 3 figures, accepted by ApJ Letter

The flat oxygen abundance gradient in the extended disk of M83
Fabio Bresolin, Emma Ryan-Weber, Robert C. Kennicutt, Quinton Goddard, arXiv:0901.1127 [ps, pdf, other]
Comments: 17 pages, 9 figures, accepted for publication in The Astrophysical Journal

Black Holes and AGN

Radiation pressure and absorption in AGN: results from a complete unbiased sample from Swift
A.C. Fabian, R. V. Vasudevan, R. F. Mushotzky, L. M. Winter, C.S. Reynolds, arXiv:0901.0250 [ps, pdf, other]
Comments: 4 pages, 2 figures, MNRAS in press

The evolution of star formation in quasar host galaxies
Stephen Serjeant, Evanthia Hatziminaoglou, arXiv:0901.0552 [ps, pdf, other]
Comments: MNRAS, accepted on 22 Dec 2008. Uses BoxedEPS (included)

Near-Infrared Spectroscopy of Seyfert Galaxies. Nuclear Activity and Stellar Population
Cristina Ramos Almeida, Ana Maria Perez Garcia, Jose Antonio Acosta Pulido, arXiv:0901.0999 [ps, pdf, other]
Comments: 44 pages, 16 figures. Accepted for publication in ApJ


Modeling and Reproducibility of Suzaku HXD PIN/GSO Background
Yasushi Fukazawa, Tsunefumi Mizuno, Shin Watanabe, Motohide Kokubun, Hiromitsu Takahashi, Naomi Kawano, Sho Nishino, Mahito Sasada, Hirohisa Shirai, Takuya Takahashi, Tomonori Yamasaki, Tomonori Yasuda, Aya Bamba, Masanori Ohno, Tadayuki Takahashi, Masayoshi Ushio, Teruaki Enoto, Takao Kitaguchi, Kazuo Makishima, Kazuhiro Nakazawa, Yuichi Uehara, Shin'ya Yamada, Takayuki Yuasa, Naoki Isobe, Madoka Kawaharada, Takaaki Tanaka, Makoto Tashiro, Yukikatsu Terada, Kazutaka Yamaoka, arXiv:0901.0419 [ps, pdf, other]
Comments: 29 pages, 45 figures, will appear on the PASJ 61, Suzaku 3rd issue

Numerical Astrophysics and Hydrodynamics

Turbulence and Magnetic Field Amplification in Supernova Remnants: Interactions Between A Strong Shock Wave and Multi-Phase Interstellar Medium
Tsuyoshi Inoue, Ryo Yamazaki, Shu-ichiro Inutsuka, arXiv:0901.0486 [ps, pdf, other]
Comments: 10 pages, 10 figures, submitted to ApJ

Stars, Star Clusters and Supernovae

An Infrared Census of Star Formation in the Horsehead Nebula
Brendan P. Bowler, William H. Waller, S. Thomas Megeath, Brian M. Patten, Motohide Tamura, arXiv:0901.0564 [ps, pdf, other]
Comments: 30 pages, 11 figures; accepted for publication in The Astronomical Journal

The Formation Rates of Population III Stars and Chemical Enrichment of Halos during the Reionization Era
M. Trenti, M. Stiavelli, arXiv:0901.0711 [ps, pdf, other]
Comments: 31 pages, 8 figures, ApJ accepted

3D modelling of the colliding winds in Eta Carinae - evidence for radiative inhibition
E. R. Parkin, J. M. Pittard, M. F. Corcoran, K. Hamaguchi, I. R. Stevens, arXiv:0901.0862 [ps, pdf, other]
Comments: 20 pages, 24 Figures, accepted to MNRAS


The distribution of stellar mass in the low-redshift Universe
Cheng Li, Simon D. M. White, arXiv:0901.0706 [ps, pdf, other]
Comments: 10 pages, 7 figures, submitted for publication in Monthly Notices

Tracing the Reionization-Epoch Intergalactic Medium with Metal Absorption Lines
Benjamin D. Oppenheimer, Romeel Davé, Kristian Finlator, arXiv:0901.0286 [ps, pdf, other]
Comments: Submitted to MNRAS, 28 pages, 19 figures

Personally I think the way they implement galactic winds as heavily mass-loaded single phase flows is simply not justified (or actually counter-indicated) by existing observational data and theoretical modeling of local starburst-driven winds. With a non-physical representation of superwinds, any wind-related results obtained in this manner can not be considered robust (they might be mildly wrong or badly wrong, and without doing it the right way its hard to know how meaningful the results are). The authors would probably argue in their defense that their method reproduces certain observational galaxy or wind-related requirements and hence is reasonable/accurate/"observationally calibrated". My response is that I dispute the robustness and applicability of those observational requirements as constraints on wind models, especially winds in the numerical form incorporated in cosmological models.

Wednesday, January 07, 2009

Charles Bolden Jr as the next head of NASA?

There is speculation that Charles Bolden Jr, a retired Marine Corps Major General and ex-astronaut (pilot of the Discovery flight in 1990 that launched the Hubble Space Telescope) may be selected by the Obama adminstration as the next head of NASA.

[Hat tip to Jim Herald]

Monday, January 05, 2009

Bob Park's take on what NASA's mission should be

In January 2nd's "What's New" (*) Bob Park at UMD presented his typically blunt view of what NASA's future should and should not involve:

In discussing NASA’s future on Tuesday, the NY Times was mesmerized by the "gap" between the end of the shuttle and the launch of a new bus to transport astronauts. Forget the damn gap. The 21st Century will be focused on planets around other suns, and on the bad news about what’s happening to our own planet. Astronauts can’t go to other stars, but we can build better telescopes and get a better look at them. Astronauts will be no help either in studying our own Sun and our own planet, Earth. We need to finish what we set out to do a decade ago, but were stopped from doing by the Bush administration: launch an updated Deep Space Climate Observatory. There is still time, but we urgently need to get started.
While some might consider this extreme, it does makes sense.

Proponents of manned space flight have got to start making a realistic case for their very expensive passion. Continuing to use empty buzzwords and catch-phrases "exploration" or "only astronauts can go fossil hunting on Mars" is not going to work on Congress and the tax-payer forever.

(*) The 01/02/09 edition was yet available on the What's New website when this post was written.

Friday, January 02, 2009

IYA2009 and other stuff...

2009 is the International Year of Astronomy, in case you didn't know, a global effort initiated by the International Astronomical Union and UNESCO.

The International Year of Astronomy (IYA2009) will be a global celebration of astronomy and its contributions to society and culture, highlighted by the 400th anniversary of the first use of an astronomical telescope by Galileo Galilei. The aim of the Year is to stimulate worldwide interest, especially among young people, in astronomy and science under the central theme "The Universe, Yours to Discover". IYA2009 events and activities will promote a greater appreciation of the inspirational aspects of astronomy that embody an invaluable shared resource for all nations.
In other astronomy-related news, Matt Springer at Built on Facts reviews Adam Frank's new book "The Constant Fire: Beyond the Science vs. Religion Debate". Nice segue between IYA2009, Galileo and Science vs. Religion eh? OK, the Catholic Church has apologized about the Galileo thing and it wasn't as simple a case of science vs religion as its often made out to be, but as the Pope's speech greeting those taking part in IYA2009 curiously doesn't mention it I thought I bring it up.

In sadder news, NASA has released its official report on the deaths of the seven astronauts killed when the space shuttle Columbia disintergrated during re-entry on Feb 01, 2003. In short, there was no way they could have survived (NYT article). The sudden loss of cabin pressure asphyxiated the astronauts and rendered them unconscious within seconds, followed by “lethal trauma occurred to the unconscious or deceased crew due to the lack of upper-body support and restraint.”

Interesting Astrophysics: Dec 29 - Jan 02

The final edition of Interesting Astrophysics for 2008, and first edition of 2009. There really isn't much this week in terms of numbers, largely thanks to their only being one release of preprints on and the email notifications from the main peer-reviewed journals don't seem to functioning this week.

Nevertheless, I firmly believe that one good starburst paper is worth a thousand normal papers, and this week its not just any starburst but the archetype M82 itself.

Galaxies and Starbursts

Near-IR spectroscopic ages of massive star clusters in M82
A. Lançon, J. S. Gallagher III, M. Mouhcine, L. J. Smith, D. Ladjal, R. de Grijs, arXiv:0812.4888 [ps, pdf, other]
Comments: 14 pages, 20 figures, uses aa.cls
Journal-ref: Astronomy and Astrophysics, 486, 165 (2008)

NIR ages between 9 - 30 Myr. This is somewhat older than typically optically-derived ages of the brighter clusters in M82. Its certainly very plausible that active star formation within the center of M82 has been going on for more than 10 Myr, but thats not quite the point that this paper is making. That optical and NIR-derived ages can differ for the same clusters... that is something people need to keep in mind when modeling the starburst (is this apparent age discrepency due to the lack of binaries in stellar population synthesis models?).

Frankly I worry about how accurate estimates of the starburst age are for even well-studied starbursts like M82 and NGC 1569. Are there any truly young starbursts (as the Wolf rayet galaxies were widely assumed to be a decade or so ago), with no significant burst star formation older than a few Myr? Are there any truly post-starburst objects with no significant star formation within the last 10-20 Myr (as NGC 1569 is widely claimed to be)?

Biases and Uncertainties in Physical Parameter Estimates of Lyman Break Galaxies from Broad-band Photometry
Seong-Kook Lee, Rafal Idzi, Henry C. Ferguson, Rachel S. Somerville, Tommy Wiklind, Mauro Giavalisco, arXiv:0812.5111 [ps, pdf, other]
Comments: 85 pages, 34 figures, submittted to ApJS

Ultraviolet Spectra of Local Galaxies and their Link with the High-z Population
Claus Leitherer, arXiv:0812.5113 [pdf]
Comments: 8 pages, invited talk given at the conference "Probing Stellar Populations out to the Distant Universe", Cefalu (Italy), September 7 - 19, 2008. To be published in the AIP Conf. Proc. Series


Dissecting Pamela (and ATIC) with Occam's Razor: existing, well-known Pulsars naturally account for the "anomalous" Cosmic-Ray Electron and Positron Data
Stefano Profumo, arXiv:0812.4457 [ps, pdf, other]
Comments: 23 pages, 14 figures, submitted to Phys.Rev.D

Maybe this should be filed under Compact Objects, but as it deals with the PAMELA and ATIC data previously interpreted as a possible Dark Matter annihilation signal it seems fitting to class this paper as Cosmology.