An Imprint of Super-Structures on the Microwave Background due to the Integrated Sachs-Wolfe Effect

Benjamin R. Granett, Mark C. Neyrinck, István Szapudi (IfA, Hawaii)

We measure hot and cold spots on the microwave background associated with supercluster and supervoid structures identified in the Sloan Digital Sky Survey Luminous Red Galaxy catalog. The structures give a compelling visual imprint, with a mean temperature deviation of 9.6 +/- 2.2 microK, i.e. above 4 sigma. We interpret this as a detection of the late-time Integrated Sachs-Wolfe (ISW) effect, in which cosmic acceleration from dark energy causes gravitational potentials to decay, heating or cooling photons passing through density crests or troughs. In a flat universe, the linear ISW effect is a direct signal of dark energy.



FIG. 1.— Stacked regions on the CMB corresponding to supervoid and supercluster structures identified in the SDSS LRG catalog. We averaged CMB cut-outs around 50 supervoids (left) and 50 superclusters (center), and the combined sample (right). The cut-outs are rotated, to align each structure’s major axis with the vertical direction. Our statistical analysis uses the raw images, but for this figure we smooth them with a Gaussian kernel with FWHM 1.4. Hot and cold spots appear in the cluster and void stacks, respectively, with a characteristic radius of 4, corresponding to spatial scales of 100 M pc/h inner circle (4 radius) and equal-area outer ring mark the extent of the compensated filter used in our analysis. Given the uncertainty in void and cluster orientations, small-scale features should be interpreted cautiously.

From the paper 'Red Nuggets at z ∼ 1.5: Compact passive galaxies and the
formation of the Kormendy Relation' by Damjanov et al (0807.1744) I chose these two plots.

We had discussions before about these tiny galaxies that Mariska and Pieter investigated. These authors do sort of the same job, but at slightly lower redshift (1.5-ish). The left plot shows the effective radius - stellar mass plane, with the dots and contours being local SDSS red galaxies. The bigger points with error bars are their (and some other) red galaxies at higher redshift, which appear to small. I show this plot, because the arrows indicate the approximate track of evolution due to three different processes: dry mergers, pure stellar mass growth without changing size and adiabatic expansion (stellar mass loss makes the systems less bound). All three processes seem incapable of transforming the galaxies towards the low - z counterparts.

The right plot shows the galaxies in the stellar mass density - effective radius plane (Kormendy relation). Here they are all on the same trend, with the high redshift galaxies smaller and denser than their local red SDSS partners. Color coding here is redshift, which appears to hint at some evolution: the higher the redshift of the galaxy, the smaller and denser it is. The main part of the evolution takes place at 1.1 < z < 1.5.

What's wrong with this picture?

(or, at least, highly suspicious--and why?):

from  Morioka et al., arXiv:0807.0101, PASJ in press.  Black dots are H-alpha emitting galaxy candidates (via a narrowband filter selection), grey regions are masked-out bright stars.  The authors use this sample to compute the clustering and luminosity function of star-forming galaxies at z=0.24, and note that the clustering in this field is stronger than in the COSMOS field.  First one to post the right answer in comments wins a beer at the next borrel.

It's the same!

From arXiv:0806.3278

Title: Correlations between MIR, FIR, H$\alpha$, and FUV Luminosities for SWIRE galaxies

Authors: Yi-Nan Zhu, Hong Wu, Chen Cao, Hai-Ning Li

The figure shows the correlation between observed H-alpha + 24 micro (y-axis, left-hand panel) and H-alpha + 8 micro (y-axis, right-hand panel) luminosities with the extinction-corrected H-alpha luminosities (x-axis) for star-forming galaxies selected from the Spitzer-SWIRE fields.

Filled circles: Normal galaxies
Open circles: Dwarf galaxies
Lines: Best nonlinear (solid) and linear (dotted) fit

SXDF SMGs & BzKs

from Takagi et al., http://arxiv.org/abs/0806.0888

The authors attempt to investigate whether submillimeter galaxies can be
identified by simple color cuts. The answer is: probably not, with the
resolution of current submm instruments.

Spectroscopic Confirmation Of An Extreme Starburst At Redshift 4.547

Capak et al., http://arxiv.org/abs/0806.0657

This is a set of images of an extreme object at z=4.5 in the COSMOS survey.  It is the most distant mm source not associated with an optically bright quasar. The rest-frame UV and Lya imaging (the first five panels on the left) show emission near the lower left of the panes, although no emission is detected in the B-band because it falls blueward of the Lyman break. At longer wavelengths, the emission shifts to the upper left; the panel on  the far right shows radio contours.

The estimated star formation rate is 1000-4000 Msun/yr, based on several indicators. The authors argue against significant AGN activity -- which would mean this SFR could be a severe overestimate -- because there is no xray detection and because an optical spectrum shows no hint of an AGN.  But, as the authors note, an AGN could lie outside the optical slit.  In fact I think this a fairly likely explanation since the authors placed the slit on the center of the UV emission (lower left), whereas an AGN would be expected to be associated with the longer wavelengths (upper right), which is where the most of the stellar mass and radio activity is.

Evidence for a Stellar-Dominated UV Background and Against a Decline of Cosmic Star Formation Beyond z~3

From Faucher-Giguere et al (http://arxiv.org/abs/0806.0372). The authors use the Lyman-alpha forest opacity to estimate the photoionizing background at 2 < z < 4.2. After subtracting the contribution from AGNs, they suggest that stellar sources are dominant (and thus may be responsible for reionization). Perhaps more remarkably, they determine a cosmic star formation rate that is flat, at odds with the well accepted Hopkins and Beacom (2006) curve.

Radio jet duty cycles in nearby galaxies

from Shabala et al., arXiv:0805.4152

This figure shows the fractile distribution of radio source ages in four different stellar mass bins. There appears to be a strong trend whereby more massive galaxies host older radio sources, suggesting that the "on phase" of radio activity lasts longer for these galaxies. The on-time and the gas cooling rate show the same dependence on stellar mass, suggesting that the two are probably linked (i.e. the availability of fuel governs whether an AGN is on or off). Elsewhere in the paper the authors argue that higher-mass galaxies also exhibit more powerful and frequent radio jets. If true, this may be further evidence for a link between radio AGN and the shutdown of star formation.

Galaxy Size Problem at z=3: Simulated Galaxies Are Too Small

(http://arxiv.org/abs/0805.3150 by M.K. Ryan Joung (Princeton), Renyue Cen (Princeton), Greg Bryan (Columbia))

The authors run zoom simulations and find the simulated galaxies are too small to match the observations after corrections (blue line, bottom panel). I suspect that their feedback isn't strong enough to disrupt the inner star formation though.

Red Galaxy Growth and the Halo Occupation Distribution

Michael J. I. Brown et al astroph 0804.2293

This is from the paper "The Halpha Galaxy Survey V. The star formation history of late type galaxies", by Phil James et al. astro-ph/0804.2167

They have SFRs from Halpha, stellar masses from K and R band photometry (all with the 1m Kapteyn Telescope) and gas masses from Westerbork neutral hydrogen observations for local late type field galaxies. Here they plot the star formation timescale (Mstar/SFR) and gas depletion timescale (Mgas/SFR) for galaxies as a function of mass and type. The dashed lines indicate the age of the universe. The fact that the star formation timescale for low mass/late type galaxies is similar to the age of the universe and their gas depletion time is much longer, whereas it is reversed for the high mass/earlier type galaxies is used as an argument that the star formation history of very late type galaxies is constant over the age of the universe and the stellar mass gradually builds up, an that for more bulgy galaxies the bulk of the star formation happens in short bursts of high SFR.

The possibility of having a higher SFR in the past is not mentioned...

Predicted OVI-galaxy cross-correlation

Figure 2 of Ganguly, Cen, Fang, Sembach, http://arxiv.org/abs/0803.4199

The authors use a CDM simulation which includes IGM metal enrichment from superwinds to predict the galaxy-OVI absorber cross-correlation at low redshifts; or, as in the figure above, the fraction of galaxies with an OVI absorber within a given distance, at different galaxy luminosities, absorber strengths, and projected absorber-galaxy separations. They find that the correlation length depends strongly on galaxy luminosity (with faint, low-mass galaxies having more nearby absorbers on average) but not on absorber strength. Only ~15% of OVI absorbers come from >L* galaxies, implying that IGM enrichment may be predominantly due to many faint sources rather than a few bright ones.

They note also that these results are somewhat preliminary and their simulation resolution may cause problems for the lowest-mass galaxies, but these will be a valuable starting point for comparison to upcoming large COS surveys.

The energy output of the Universe from 0.1 micron to 1000 micron

From http://arxiv.org/abs/0803.4164.

Evolution of the field galaxy pair fraction

Figure 13 of Hsieh et al., http://arxiv.org/abs/0804.1604

This plot shows the average number of galaxy companions as a function of redshift for different pair separations. With increasing separations, the evolution of the pair fraction decreases. Assuming these pairs represent early-stage mergers, this may imply that the infall/merging timescales are changing with redshift: at high redshift it takes longer for a galaxy to finish merging (i.e. go from 20 kpc to 0 kpc) than at low redshift, relative to the inital (r=150 to 50 kpc) infall. The authors suggest that such a change in timescale may be due to dark matter halos at lower redshift being more concentrated: since the density is lower in the outskirts of highly-concentrated halos, the dynamical friction timescale at large radii is longer, and therefore one might expect merging galaxies to spend more time at larger radii (thus increasing the large-separation pair fraction) at lower redshifts.

The MBH-Sigma relation in the last six billion years

Figure 2 from Woo et al., astro-ph 0804.0235

The M_BH-sigma relation of active galaxies.
Left panel: local Seyferts with sigma from Greene & Ho (2006) and our own M_BH estimates consistently calibrated with our estimates for distant samples (black circles); local Seyferts with M_BH, measured via reverberation mapping (Onken et al. 2004; magenta circles)
Right panel: new measurements at z=0.57 (red stars); Seyfert galaxies at z=0.36 from our earlier work (blue circles). The local relationship of quiescent galaxies (Tremaine et al. 2002; black points) are shown for comparison as a solid (Tremaine et al. 2002) and dashed (Ferrarese & Ford 2005) line.

From http://arxiv.org/abs/0803.3944. The author postulates that a natural explanation for the observed metallicity gradient in DLAs can be explained via dense, metal poor disks and less dense metal rich outflows.

Star formation in BCGs

(Figure 10 of O'Dea et al., http://arxiv.org/abs/0803.1772)

Upper limits on the mass deposition rate (derived from X-ray emission measurements) vs. star formation rate for brightest cluster galaxies. Filled circles denote the maximum mass deposition rate (assuming no gas heating), while open circles are the rates derived from detailed cooling-flow model fits.

This paper discusses results from a Spitzer survey of 62 brightest cluster galaxies that exhibit optical line emission, specifically the ~50% of those galaxies that show excess infrared emission. While four of these appear to be dominated by AGN, they claim that the remainder show evidence for star formation (from L_IR, CO measurements, and Halpha luminosity). The above figure then appears to show a strong correlation between mass deposition from the ICM and star formation, and therefore such cooling may be the fuel source for the SF activity in these galaxies. Furthermore, the MDR exceeds the SFR, indicating that some reheating mechanism may be at work. It should be noted that all the points in this figure are formally upper limits, so in fact the cooling rate could be entirely consistent with the SFR.

arXiv:0803.1489 [ps, pdf, other]

Title: The contribution of star formation and merging to stellar mass buildup in galaxies

Authors: Niv Drory (1), Marcelo Alvarez (2) ((1) MPE, Garching, Germany, (2) KIPAC-Stanford, USA)

Comments: Accepted for publication in ApJ

Subjects: Astrophysics (astro-ph)

The authors take data from the FORS Deep Field (FDF), 5500 galaxies with redshifts between 0 and 5. They obtain stellar masses and SFRs as well as photo-z's. By integrating the SFR over time they calculate, as a function of mass, the change in number density of galaxies of that mass due to star formation. They compare that to the actual change of the mass function to obtain the contribution that is from anything other than star formation, being mainly merging and accretion (assuming that tidal stripping and so on are negligable). They call this the assembly rate and that is what is shown in the figure (the y-axis normalized to have the relative change), as a function of z and mass (in both plots). See the paper for selection effects...

Are SNIa a two-component family?

In astro-ph/0803.1130, Dahlen, Strolger & Riess report on their HST survey for high redshift SN Ia. Their results strengthen the argument that the SNIa rate drops at high redshift. The immediate interpretation of this is that SN Ia only start after some long delay. Their favourite model has a delay time of 3.7 Gyr and is shown as the solid line in the Figure. The solid points in the Figure shows the observed SN Ia rate.

Now the problem is that a number of groups have recently argued, fairly convincingly, that SN Ia at lower redshift clearly fall into two categories: A group of delayed explosions and a group of "prompt" explosions - ala SN II. Three such models are shown as non-solid lines in the Figure and the match to the observations fails to excite :) What gives? The authors argue that dust obscured star formation might explain the differences, but it is not settled.

The evolution of submillimetre galaxies: two populations and a redshift cut-off

Wall, Pope, & Scott 2008, MNRAS, 383, 435

These authors find reasonably secure counterparts for 35/38 SCUBA sub-mm sources in GOODS-N. This plot shows the relationship between redshift (combination of spectroscopic and photometric redshifts) and rest-frame 850 micron luminosity (which is also illustrated by the size of the circular plotting symbols). The black symbols are those below the median luminosity, and the blue symbols are above.  The curves show the detection limits; since the noise varies strongly over the SCUBA map, a different completeness curve is shown for the location on the map of each detected galaxy.  The fact that these curves flatten at high redshift is due to the negative K-correction.

One notes an apparent lack of high-luminosity sources at z<~1.5 and of low-luminosity sources at z>~2.5.  This is interpreted as an aspect of the generic downsizing trend of star-formation.  The authors split the sample in half by luminosity, and model the evolution of the luminosity function of the two samples independently as a function of redshift.  But the qualitative conclusions remain the same, and based on the data you'd have to be pretty brave to conclude very much more than that.  I'll post a few more thoughts in the comments, but those will probably only be relevant to those who have actually taken a look at this paper.