D'Onghia, Springel, Hernquist & Keres, "Substructure depletion in the milky way halo by a disk". The put a disk in a cosmologically simulated halo, by hand and observe a lot of stripping of the mass of subhaloes by disk shocking. This reduces the amount of substructure in the inner halo and may help solving the missing satellite problem...

Narrow-line AGN and their host galaxies

from Greene et al., arXiv:0907.1086

In this paper several aspects of 0.1<z<0.4 narrow-line (obscured) AGN
and their host galaxies are investigated. The sample was selected
from the SDSS and higher-quality follow-up spectra were taken with
Magellan; derived properties include AGN line widths, stellar velocity
dispersions, and Eddington ratios.

The plot above is particularly notable, showing the [OIII] width (i.e.
gas velocity dispersion) compared to the stellar velocity dispersion.
There's no apparent correlation, indicating that gas in the galaxy is
very much out of equilibrium with the stars; from this the authors
conclude that the AGN must be affecting the gas properties on a
galaxy-wide scale.

The diversity of type 1a supernovae from broken symmetries

Stellar mass growth over cosmic time

Several authors have found that the SFR of star-forming galaxies is approximately proportional to stellar mass to the first power, and that the constant of proportionality decreases with redshift. Using such a relation, it is straightforward to parameterize the growth of a galaxy
(ignoring major mergers) given it's observed redshift and stellar mass.

This letter by Alvio Renzini, discusses this issue. Renzini takes a recent parameterization of the SFR from the literature, and estimates how a galaxy at z=3 (when the universe was 2Gyr old) will grow. The upper red curve in the plot above shows the growth of stellar mass for the published parameterization... but obviously a typical observed galaxy can't grow in mass by 5 orders of magnitude from z=3 to z=0. So the lower red curves show how the growth will occur if you reduce the SFR at all redshifts by a factor of \eta.

The letter goes on to briefly discuss how environment, mergers, and morphological transformations/quenching will affect galaxy growth.

Velocity dispersion at z~2

from van Dokkum, Kriek, & Franx 2009, http://arxiv.org/abs/0906.2778

This paper presents the first directly-measured velocity dispersion of a compact quiescent galaxy at z~2. A dispersion of 510 (+165, -95) km/s is measured by fitting galaxy templates to an ultra-deep near-IR (Gemini) spectrum; the dispersion uncertainty is calculated through Monte Carlo simulations.

Such a high dispersion is unparalleled in the local universe, as shown in the figure above. Candidate high-sigma objects were already known, but the dispersions in these cases were indirect (inferred from masses and radii) and so it was conceivable that systematic effects could have been at play. Reassuringly, the stellar masses inferred from SED fitting and the velocity dispersion are in decent agreement with each other, so the previous results apparently are not just due to severely overestimated masses.

A new type of stellar explosion

From Perets et al. (arXiv:0906.2003) Caption reads:
"Comparison of the SN 2005E ejecta mass and luminosity with other SNe [SNe Ia, squares;
SNe Ib/c, × marks; SNe II, circles]. The lower panel shows the total ejecta mass inferred for SN 2005E, which is the lowest inferred ejecta mass found for any SN, based on nebular spectra. Its position in the luminosity vs. ejecta-mass phase space is unique, suggesting it is not a member of currently well-known SN families. The middle panel shows the Ni mass inferred for SN 2005E. The small Ni mass inferred for SN 2005E is consistent with its low luminosity, although somewhat lower than might be expected from the extension of the observed Ni mass-luminosity relation observed for other SNe (dashed line and formula). The upper panel shows the Ni ejecta mass fraction MNi/Mtotal inferred for SN 2005E. The sources from which the SN data were collected are listed in the SI, Section 8."

This is a supernova that doesn't match any of the known classes. It was not found in a star forming region, so core collapse seems unlikely. It also ejected significantly less mass than any known SNIa. It has a very high Ca yield.

First direct metallicity at z>1

from Yuan & Kewley, http://arxiv.org/abs/0906.0371

The authors use MOIRCS on Subaru to obtain a near-IR (rest-frame optical) spectrum of a strongly-lensed z=1.7 galaxy, and detect the [OIII] 4363A line, the first such detection at z>1. This line provides a direct measurement of the oxygen abundance; the above plot shows this measurement (red) compared to z>2 galaxies (from Erb et al.; black points) and the local relation (dashed line). While the z>2 data suggested a steeper slope in the metallicity-mass and metallicity-luminosity relations at high redshifts, with the new data point it actually doesn't look much different from at z=0. Of course, caveats about different techniques (the z>2 metallicities were not determined with the same technique) and redshifts apply.

AGN activity in nearby galaxies

from Goulding & Alexander, http://arxiv.org/abs/0906.0772

The authors describe a volume-limited survey of all (64 in total) IR-
luminous (L_IR>3e9) galaxies within 15 Mpc with Spitzer-IRS. The
goal is to look for the [NeV] line at 14um, which is considered to be
an unambiguous tracer of AGN activity since the ionization potential
of this line is generally too high to produce in HII regions.

The BPT diagram above shows SDSS galaxies (faint grey points),
galaxies from their sample with no detected [NeV] (black squares),
and those with detected [NeV] (red squares). Dividing lines between
star-forming galaxies, LINERs, and Seyferts are also overplotted.
Although only 7 galaxies strictly meet the "Seyfert" classification
based on their optical emission lines, 17 show [NeV]; the authors
conclude that the BPT diagnostic misses more than half of AGN
activity in IR-luminous galaxies. However, most of the "optical non-
AGNs" classify as LINERs, so it seems a bit much to say they were
totally "missed" by the BPT diagnostic. Also, in a subsequent plot
it's apparent that most of these near-IR AGN are extremely weak -
between 1-5% of the total galaxy luminosity. However, there's
marginal evidence for a correlation between AGN activity and L_IR
(hence star formation) in this sample.

In 0906.0590, Kistler et al investigate "The star formation rate in the reionization era as indicated by gamma-ray bursts". They make a compilation of high redshift long gamma ray bursts, deduce a correction factor as a function of redshift (at intermediate redshifts) between the rate of GRBs and the SFR and calculate the SFR(z), from GRBs. The result is the Lilly-Madua plot shown. The upper yellow points are results from the GRBs. Note that in all four bins there are just a few (1 in the last) GRBs used for the calculation. The grey points are the well known Hopkins & Beacom (2006) compilation, while the other, higher redshift, coloured points are deductions from UV luminosity functions from LBGs (Bouwens et al 2008) and Lyman alpha emitters (Ota et al 2008)

The grey lines with positive slope are the SFRDs necessary to keep the universe ionized according to Madau et al 1999. This seems to indicate that the star formation alone is enough to keep the universe ionized from z~8.

Clustered star formation as a natural explanation of the Halpha cutoff in disc galaxies

From Pflamm-Altenburg and Kroupa (arXiv:0905.0898v1)
Caption reads:
"The Hα-luminosity surface density versus the total gas surface density observed for seven disc galaxies15 averaged over annuli at different galactocentric radii is plotted (black squares) after correcting for photon leakage from H ii regions (see Supplementary Discussion). These galaxies have a mean star formation rate of SFR=6.9 M⊙ yr−1 (3.2 – 16.4 M⊙ yr−1 )2, 15 , a mean total gas mass of Mgas = 2.1 · 1010 M⊙ (0.6 – 3.6 · 1010 M⊙ )2, 15 and a mean scale length of rd = 4.4 kpc (3.9 – 5.2 kpc)25–28 . These mean values define our model standard disc galaxy. For a choice of γ = 2 the LIGIMF-theory predicts an ΣHα -Σgas relation which matches the observations excellently (solid line). Note that the underlying true star-formation density as derived from UV observations1 is directly proportional to the gas surface density (N = 1) and is shown after converting it into an Hα surface luminosity using the wrong linear Kennicutt Hα-SFR relation2, 29 (dashed line) and shows the expected ΣHα -Σgas relation based on the classical picture which is in disagreement with the observations."
Basically, since stars form in clusters, and because you have lower mass star clusters at lower densities, you expect relatively less massive stars and therefore a Hα cutoff

The statistical nature of the brightest cluster galaxies

The brightest cluster galaxies (BCGs) lie at the center of clusters, and have very different properties than normal early-type galaxies.  They have flatter brightness profiles, with envelopes that extend well out into intra-cluster space, and have extremely large stellar masses.  Additionally, the luminosity function of cluster galaxies tends to show a bump at large luminosity, which corresponds to the BCGs.  Obviously, BCGs must form differently than other early-types.  But one can still ask the question, are BCG luminosities consistent with being drawn from the overall cluster population?

This issue has been visited several times in the past, and now most recently by Lin, Ostriker, & Miller using clusters detected in SDSS.  Their basic method is to create mock clusters by scrambling the galaxies among the observed clusters, and then to compare the luminosities of the brightest galaxies in the mock clusters to the luminosities of the actual BCGs.  The purple circles in the top panel of this figure show the observed BCG luminosities as a function of total cluster luminosity.  The squares show the BCG luminosities using a running mean, and the green crosses show the running mean computed from the mock clusters.  It appears that BCGs are more luminous than expected based on the mock clusters, a difference that becomes more apparent at high luminosities.

This conclusion is also apparent in the bottom panel, which shows the difference between the observed BCG luminosities and the the expected luminosity (filled purple symbols), compared to the difference observed in one realization of the mock cluster sample (open red).

The authors conclude that, in a flux limited sample of LRGs, BCGs will become more dominant at high redshifts.  So baryonic accoustic oscillation studies will have to take this into account.

A NEW TEST OF THE STATISTICAL NATURE OF THE BRIGHTEST CLUSTER GALAXIES

In arXiv:0904.3098 Lin, Ostriker & Miller use a cluster catalog, assemblked from SDSS DR5 to examine the question whether or not BCGs are just the statistical extremes from the luminosity distributions of cluster galaxies, or whether they are really distinct objects. They do a very simple test: they throw together all cluster galaxies, and randomly sample luminosities from this distribution, adding up to the total luminosities of clusters. They then compare the statistic d in this plot. d is the difference in log between the mean luminosity of observed(blue)/sampled(red) BCGs and of 200 MC realizationsof this process. The red line therefore should be centered on zero, and it is. The offset of the blue histogram is significant in the total sample (494 clusters) and in the sample of bright clusters (124 clusters). FOr the total sample they calculate a probablity of less than 0.8% that the distributions come from the same parent distribution, for the bright subsample it is 0.03%. For low luminosity clusters there is no significant deviation between the two (P = 54.5%). They therefore claim that (at least for the bright ones) BCGs must evolve distinct from the rest of the galaxy population, making them brighter than their non-BCG cluster companions.

Early Assembly of the Most Massive Galaxies

In this Nature paper, Collins et al. compare the stellar masses of brightest cluster galaxies (BCGs) at z=1-1.5 to BCGs at z~0 and to the predictions from semi-analytic models.  This figure shows the observed masses (red circles; the red cross shows the mean value) compared to the mean mass for a low-redshift sample (dashed line).  It also shows the masses of BCGs in the semi-analytic models (grey diamonds are the masses of individual galaxies, and the black circles are the mean).  It seems that the high-redshift BCGs have already accumulated essentially all of their mass, with very little of the additional growth that is predicted by the models. 

Interestingly, the authors state that two of the BCGs may be undergoing major mergers, which will make them even more massive.

One worry I have is that this analysis relies on matching the high-redshift cluster sample to an appropriate local sample.  The authors don't discuss this matching in detail.  If the local sample was selected to have the same total cluster mass (which I think is the case), then all that the authors have shown is that the ratio of BCG stellar mass to total cluster mass doesn't evolve with redshift.  But, as the authors note (although in a different context), previous studies have already arrived at this conclusion out to z~0.8.

There are other uncertainties in this analysis.  The authors use a crude method to estimate the stellar masses (they seem to use only one or two observed bands).  Additionally, it is well-known that the total mass of extended low-redshift galaxies is difficult to measure (the authors don't address this issue).

BLAST off

The non-ironic DVD cover:

The science:

Figure 9 of Pascale et al., http://arxiv.org/abs/0904.1206

The Balloon-borne Large-aperture Submillimeter Telescope (BLAST) released a slew of papers on astro-ph today. This instrument has surveyed 8.7 deg2 in GOODS and ECDFS at 250, 350, and 500 microns.  The authors also incorporate IRAC and MIPS data from SIMPLE and FIDEL, and select sources based on 24um flux. The additional wavelength coverage from BLAST allows the authors to better constrain L_IR as well as directly constrain the average dust temperatures of sources as a function of redshift. It turns out that the cosmic IR background can be almost (or entirely) resolved into individual sources, with most of the 70um background coming from z<1 galaxies and the 500um background coming from z>1.

The above plot shows the inferred star formation density evolution from this study (black circles), UV/optical measurements (triangles; dashed error bars have extinction corrections applied). About 70% of their 24um sources had reliable UV/NIR photometric redshifts, and the remaining 30% were estimated through IRAC SED fitting; the grey circles show the SFH with these "IRAC redshifts" excluded. The solid and dashed lines show a luminosity function model with (dashed) and without (solid) taking into account the 24um flux limit of 20 microJansky. As the BLAST measurements fall below the model at thehighest redshifts, the authors conclude that they're missing a population of faint 24um sources.

Black hole M-sigma relation

This is a guest post from Brent:

Figure 1 from "The M-sigma and M-L Relations in Galactic Bulges and Determinations of their Intrinsic Scatter" by Gueltekin et al. (http://arxiv.org/abs/0903.4897v1):

Caption (Abridged): "The M–sigma relation for galaxies with dynamical measurements. The symbol indicates the method of BH mass measurement: stellar dynamical (pentagrams), gas dynamical (circles), masers (asterisks). Arrows indicate 3sigma_68 upper limits to BH mass. The color of the error ellipse indicates the Hubble type of the host galaxy: elliptical (red), S0 (green), and spiral (blue). The saturation of the colors in the error ellipses or boxes is inversely proportional to the area of the ellipse or box. Squares are galaxies that we do not include in our fit. The line is the best fit relation to the full sample: MBH = 108.12 Msun (sigma/200 km s−1 )4.24. The mass uncertainty for NGC 4258 has been plotted much larger than its actual value so that it will show on this plot."

Interesting Plot showing the latest and most reasonable collection of galaxies with dynamical BH mass estimates, along with a statistically sound investigation of the Msigma relation and its intrinsic scatter. They find a scatter of (log-normal) e_0=0.44±0.06 (0.31±0.06 for ellipticals only), which could be physical or systematic uncertainties in the observations.

High z Low Z Galaxies

From Salzer et al. (arXiv:0903.3948). Caption reads: Luminosity-metallicity relation for 1300+ low-z KISS galaxies (z < 0.095; small dots) and the 13 [O III]-detected star-forming
KISS galaxies (red squares). The solid line is a linear fit to the low-z galaxies, while the lower dashed line has the same slope but fits the higher-z galaxies with an offset of -1.1 dex.

These galaxies have redshifts in the range 0.29-0.42. Such luminous galaxies at such low metallicities pose problems for galaxy evolution models, as the evolution in metallicity at these redshifts is expected to be mild.

Dissecting the fundamental plane

In arxiv.org/0903.3603, Graves et al. dissect the red sequence. They use low redshift red sequence galaxies from the spectroscopic sample. They bin in central stellar velocity dispersion, effective radius and residual central surface brightness. Here they show three panels, the fundamental plane (FP) midplane, and stuff with lower central SB, and higher SB. Color indicates the mean luminosity weighted age of the stellar population. The diagonal dashed lines indicate constant dynamical mass. The near vertical structure in the color scale indicates that the mean age is a much stronger function of veloicty dispersion than of effective radius and/or dynamical mass. This implies that the velocity dispersion is a better indicator of stellar age, and thus that stelar velocity dispersion and dynamical mass should not be considered 'the same'.

This result is consistent with merger siulations in which the effective radius depends mainly on orbital parameters of the merging galaxies.

Galaxies at high surface brightness are younger, implying that the thickness of the FP is real (i.e. has a physical origin).

An SMG with A_V>~5

One of the brightest sub-mm galaxies (SMGs) in the GOODS-N field is completely undetected in deep optical/NIR imaging.  Guessing that this object might be part of a known protocluster at z=4.05, Daddi et al. have used the IRAM Plateau de Bure Interferometer to search for CO emission in the expected wavelength range.  This figure shows that they found it.

This is quite a remarkable object: the sub-mm emission corresponds to a star formation rate of order 1000 Msun/yr, and the SED suggests stellar mass of roughly 10^11 Msun and A_V in the range 5-7.5.  That's a lot of extinction.

Inside-out galaxy growth?

Figure 1 from Bezanson et al., http://arxiv.org/abs/0903.2044

The authors investigate possible mechanisms for the size and surface
density evolution from z=2.3 to the present. The above figure shows
average stellar density profiles of ellipticals at z=0 (colored
lines, representing different masses) and at high redshift (grey
shaded region). At small radii the profiles match pretty well, but
farther out they diverge rather drastically. This suggests that the
compact high-redshift quiescent galaxies may be the cores of massive
ellipticals in the local universe, growing from the inside out via
minor mergers. (later in the paper the authors show that major
mergers can't produce the observed evolution in the mass-size relation).

Evolution of Lyman alpha halos around HzRG

Zirm, Dey, Dickinson, Norman
ApJ 2009, 694, L31

Summary: The authors take STIS spectra of 5 z=1 HzRGs. 4 show extended Lyman alpha emission. The Lyman alpha halos that surround these z=1 HzRGs are smaller, and less luminous than those that surround z>2 HzRGs. The authors claim this is due to evolution of these massive galaxies. The z=1 halos are not ionized by shock heating of the infalling gas (as in the high-z halos), but rather by the AGN and star formation.