66 research outputs found
On the Spin Bias of Satellite Galaxies in the Local Group-like Environment
We utilize the Millennium-II simulation databases to study the spin bias of
dark subhalos in the Local Group-like systems which have two prominent
satellites with comparable masses. Selecting the group-size halos with total
mass similar to that of the Local Group (LG) from the friends-of-friends halo
catalog and locating their subhalos from the substructure catalog, we determine
the most massive (main) and second to the most massive (submain) ones among the
subhalos hosted by each selected halo. When the dimensionless spin parameter
(lambda) of each subhalo is derived from its specific angular momentum and
circular velocity at virial radius, a signal of correlation is detected between
the spin parameters of the subhalos and the main-to-submain mass ratios of
their host halos at z=0: The higher main-to-submain mass ratio a host halo has,
the higher mean spin parameter its subhalos have. It is also found that the
correlations exist even for the subhalo progenitors at z=0.5 and z=1. Our
interpretation of this result is that the subhalo spin bias is not a transient
effect but an intrinsic property of a LG-like system with higher main-to-
submain mass ratio, caused by stronger anisotropic stress in the region. A
cosmological implication of our result is also discussed.Comment: Accepted for publication in JCAP, 15 pages, 12 figures, dimensionless
spin parameter of each subhalo determined from its circular velocity measured
at the virial radius, the correlations between the spin parameters of the
subhalo progenitors and the main-to-submain mass ratios of their descendant
hosts newly determined, minor mistakes correcte
Bursty stellar populations and obscured AGN in galaxy bulges
[Abridged] We investigate trends between the recent star formation history
and black hole growth in galaxy bulges in the Sloan Digital Sky Survey (SDSS).
The galaxies lie at 0.01<z<0.07 where the fibre aperture covers only the
central 0.6-4.0kpc diameter of the galaxy. We find strong trends between black
hole growth, as measured by dust-attenuation-corrected OIII luminosity, and the
recent star formation history of the bulges. We conclude that our results
support the popular hypothesis for black hole growth occurring through gas
inflow into the central regions of galaxies, followed by a starburst and
triggering of the AGN. However, while this is a significant pathway for the
growth of black holes, it is not the dominant one in the present-day Universe.
More unspectacular processes are apparently responsible for the majority of
this growth.
In order to arrive at these conclusions we have developed a set of new high
signal-to-noise ratio (SNR) optical spectral indicators, designed to allow a
detailed study of stellar populations which have undergone recent enhanced star
formation. Working in the rest-frame wavelength range 3750-4150AA, ideally
suited to many recent and ongoing spectroscopic surveys at low and high
redshift, the first two indices are equivalent to the previously well studied
4000AA break strength and Hdelta equivalent width. The primary advantage of
this new method is a greatly improved SNR for the latter index, allowing the
present study to use spectra with SNR-per-pixel as low as 8.Comment: 27 pages, submitted to MNRAS. Due to astro-ph size restrictions 6
figures in appendix are available as separate files. Full version, with full
resolution figures available at
http://www.mpa-garching.mpg.de/~vwild/HDelta/Hd_PCAmethod.pd
IVOA Recommendation: VOResource: an XML Encoding Schema for Resource Metadata Version 1.03
This document describes an XML encoding standard for IVOA Resource Metadata,
referred to as VOResource. This schema is primarily intended to support
interoperable registries used for discovering resources; however, any
application that needs to describe resources may use this schema. In this
document, we define the types and elements that make up the schema as
representations of metadata terms defined in the IVOA standard, Resource
Metadata for the Virtual Observatory [Hanicsh et al. 2004]. We also describe
the general model for the schema and explain how it may be extended to add new
metadata terms and describe more specific types of resources
The Varied Fates of z~2 Star-forming Galaxies
Star-forming galaxies constitute the majority of galaxies with stellar masses
>10^10 M_Sun/h^2 at z~2 and dominate the star-formation rate density of the
Universe at this early epoch. It is thus critical to understand their origins,
evolution, and connection to the underlying dark matter distribution. To this
end, we identify the dark matter halos (including subhalos) that are likely to
contain star-forming galaxies at z~2 (z2SFGs) within a large dissipationless
cosmological simulation and then use halo merger histories to follow the
evolution of z2SFG descendants to z~1 and z~0. The evolved halos at these
epochs are then confronted with an array of observational data in order to
uncover the likely descendants of z2SFGs. Though the evolved halos have
clustering strengths comparable to red galaxies at z~1 and z~0, we find that
the bulk of z2SFGs do not evolve into red galaxies, at either epoch. This
conclusion is based primarily on the fact that the space density of z2SFGs is
much higher than that of lower redshift red galaxies, even when accounting for
the merging of z2SFG descendants, which decreases the number density of z2SFG
descendants by at most a factor of two by z~0. Of the ~50% of z2SFGs that
survive to z~0, ~70% reside at the center of z~0 dark matter halos with M>10^12
M_Sun/h. Halo occupation modeling of z~0 galaxies suggests that such halos are
occupied by galaxies with M_r<-20.5, implying that these z2SFGs evolve into
``typical'' ~ L* galaxies today, including our own Galaxy. The remaining ~30%
become satellite galaxies by z~0, and comparison to halo occupation modeling
suggests that they are rather faint, with M_r<-19.5. (ABRIDGED)Comment: 13 pages, 5 figures. ApJ in pres
Quenching of Star Formation
In the last decade we have seen an enormous increase in the size and quality
of spectroscopic galaxy surveys, both at low and high redshift. New statistical
techniques to analyse large portions of galaxy spectra are now finding favour
over traditional index based methods. Here we will review a new robust and
iterative Principal Component Analysis (PCA) algorithm, which solves several
common issues with classic PCA. Application to the 4000AA break region of
galaxies in the VIMOS VLT Deep Survey (VVDS) and Sloan Digital Sky Survey
(SDSS) gives new high signal-to-noise ratio spectral indices easily
interpretable in terms of recent star formation history. In particular, we
identify a sample of post-starburst galaxies at z~0.7 and z~0.07. We quantify
for the first time the importance of post-starburst galaxies, consistent with
being descendants of gas-rich major mergers, for building the red sequence.
Finally, we present a comparison with new low and high redshift "mock
spectroscopic surveys" derived from a Millennium Run semi-analytic model.Comment: 7 pages, 3 figures. Conference proceedings in "Classification and
Discovery in Large Astronomical Surveys", 2008, C.A.L. Bailer-Jones (ed.
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