Friday, 29 February 2008

Line-of-sight CIV and MgII absorber distributions

from Wild et al.,

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

The color bimodality in galaxy clusters sinze z=0.9

Authors: Loh, Ellingson, Yee et al.

The red fraction as a function of redshift for galaxies with r/r200 < 0.25 (core), 0.25 <
r/r200 < 0.5, 0.5 < r/r200 < 1.0 and 1.0 < r/r200 < 2.0 (outskirts) and brighter than M⋆ + 1.5.

Galaxies in 1000 clusters from the Red Sequence Cluster Survey. They investigate the Butcher-Oemler effect in clusters and the radial dependence of it. They find that the evolution (incresing red fraction with decreasing redshift) is found at all radii, but strongest in the outskirts. The blue population in the outskirts might be an infalling population of galaxies, gradually tarnsforming into red galaxies. Not visible from the plot, but yet another conclusion: starburst type galaxies are less than 5% of all galaxies in the clusters, and therefore the galaxies making up the blue population are not likely to be a population of starbursting dwarfs.

Friday, 22 February 2008

Kinemetry of SINS High-Redshift Star-Forming Galaxies: Distinguishing Rotating Disks from Major Mergers

Shapiro et al.

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.

Gemini and Hubble Space Telescope Evidence for an Intermediate Mass Black Hole in omega Centauri

Eva Noyola (1,2), Karl Gebhardt (2), Marcel Bergmann (3)

Friday, 8 February 2008

Black hole growth and stellar assembly at high-z

Figure 1 in Polletta (2008, arXiv:0802.0693)
The relative luminosities produced by stars (H-band) and by AGN-heated dust (5 um) in three classes of AGNs are compared. The three classes are high-z radio galaxies (HzRGs, blue circles), sub-millimeter detected AGNs (SMG/AGN, green triangles) and IR-selected obscured QSOs (IsOQ, red crosses). The diagonal lines indicate expected luminosities for various black hole masses assuming a variety of values for the Eddington ratio (lambda) and offsets to the local M_bh-M_star relation (delta).

There is a segregation between the luminosities of the three classes, which can be attributed to the different classes of AGNs emitting at different Eddington ratios or that they follow different M_bh-M_star relations. Also evolution from IsOQs to SMG/AGNs is suggested as the bulk of stellar mass is still being assembled in the former, whereas the bulge is at a more advanced stage for the HzRGs and SMG/AGNs hence possibly representing a later phase in AGN evolution.