These plots show the linear number densities of narrow CIV (left) and
MgII (right) seen in SDSS QSO spectra. On average an excess of
absorbers is seen near QSOs with a high-velocity tail in CIV, and the
authors address the question of whether these are due to galaxy
clustering (i.e. gas in the halos of galaxies near the QSOs) or
intrinsic to the AGN by attempting to model these distributions.
Three components are included in their model: galaxy clustering,
peculiar velocities, and the radius within which the QSO photoionizes
the absorbers.
In both plots, the dashed blue line shows the predicted number of
absorbers assuming only galaxy clustering (with photoionization radii
of 0.18 Mpc and 0.8 Mpc for CIV and MgII respectively). While
provides a good fit to MgII, it cannot predict the high-velocity tail
of CIV absorbers. The solid black line in the left-hand plot shows
the predictions from their full model, with the clustering component
from this model shown as the red line. The spike of CIV absorbers
seen near v=0 thus appears to consist of about 55% external galaxies
and 45% intrinsic quasar absorbers, while the high-velocity tail is
entirely due to intrinsic absorption. Also, it's notable that the
ionization radius for MgII (0.8 Mpc) is much larger than typical QSO
host halos, implying that the quasars also destroy MgII in external
galaxies.
We present a simple set of kinematic criteria that can distinguish
between galaxies dominated by ordered rotational motion and those
involved in major merger events. Our criteria are based on the
dynamics of the warm ionized gas (as traced by H-alpha) within
galaxies, making this analysis accessible to high-redshift systems,
whose kinematics are primarily traceable through emission features.
Using the method of kinemetry (developed by Krajnovic and co-workers),
we quantify asymmetries in both the velocity and velocity dispersion
maps of the warm gas, and the resulting criteria enable us to
empirically differentiate between non-merging and merging systems at
high redshift. We apply these criteria to 11 of our best-studied rest-
frame UV/optical-selected z~2 galaxies for which we have near infrared
integral field spectroscopic data from SINFONI on the VLT. Of these 11
systems, we find that >50% have kinematics consistent with a single
rotating disk interpretation, while the remaining systems are more
likely undergoing major mergers. This result, combined with the short
formation timescales of these systems, provides evidence that rapid,
smooth accretion of gas plays a significant role in galaxy formation
at high redshift.
Figure 1 in Polletta (2008, arXiv:0802.0693)
Figure 5 in Noterdame et al (2008, arXiv:0801.3682)
(Figures 1+2 of Croton & Farrar, arXiv:0801.2771)Not from anywhere particularly inspiring, apparently. The authors
investigate red and blue galaxy populations in voids using the
Millennium simulation. On the left are the predicted Millennium
galaxy luminosity functions (solid lines) and observed 2dF LFs for
the global sample (solid points) and voids (open circles). The right-
hand plot shows the predicted and observed LFs of red and blue void
galaxies, with galaxies at the centers of their halos (i.e. non-
satellites) shown as a dotted red line.
A "radio-mode" feedback model, efficiently quenching star formation
above a threshold halo mass but independent of environment, was
employed and tuned to fit only the global 2dF luminosity function.
As the left panel shows, this more or less automatically matches the
void galaxy LF as well, and reproduces the relative red and blue void
populations reasonably well (right panel). The authors conclude
there is no unusual physics going on in void galaxy formation, and
further that the presence of "red and dead" void galaxies is not
actually a big problem for galaxy formation models. As in denser
environments, red galaxies are simply those that occupy the most
massive halos.
These authors identify overdense regions up to z~2.5 in GOODS-S using photometric redshifts. The most interesting feature is a proto-cluster at z~1.6. This figure shows the distribution of rest-frame color, mass, and M_B for candidate members of this proto-cluster (open histograms) and for field galaxies at similar redshift (filled histograms).
The candidate cluster galaxies tend to be brighter and more massive. There is also a prominent red sequence (and I suspect that the effect of interlopers is to contribute to the blue cloud, so the red sequence is probably even more prominent than is immediately apparent). These characteristics have been seen before at high-z, but this is a nice illustration and it is neat that they are able to do this kind of thing using photometric redshifts.
In this letter, the author distinguishes between morphology (i.e. early- vs. late-type) and structure (quantified using Sersic index). Although these two properties are correlated with each other, it turns out that it is meaningful to consider them separately. In the scheme used in this letter, a galaxy is classified as early-type if it has a smooth light distribution, even
if the Sersic index is small. Conversely, a galaxy is classified as late-type if the light distribution is clumpy even if it has a high Sersic index.
The bottom panels show a strong relationship between galaxy structure (Sersic index) and stellar mass, with little residual dependence on environmental density. The top panels show a relationship between morphology (i.e. smoothness) and environmental density, with essentially no residual dependence on mass.
The key to interpreting these results is to realize that star formation tends to make the light distibution clumpy. So (specific) star formation rate depends on environmental density, while structure depends only on stellar mass.
I found this interesting because it seems to imply that whatever processes are responsible for reducing the star formation in dense regions are ~independent of the processes that determine galaxy structure.
From 0801.1170. The luminosity-halo mass relation for brightest cluster galaxies, Brough et al.
Figure 2 in arXiv:0801.1594, Wilkins et al.
(Figure 6)
Figure 6 in arXiv:0801.1193
