50 research outputs found
How Do Galaxies Get Their Gas?
We examine the temperature history of gas accreted by forming galaxies in SPH
simulations. About half the gas shock heats to roughly the virial temperature
of the galaxy potential well before cooling, condensing, and forming stars, but
the other half radiates its acquired gravitational energy at much lower
temperatures, typically T<10^5 K, and the histogram of maximum gas temperatures
is clearly bimodal. The "cold mode" of gas accretion dominates for low mass
galaxies (M_baryon < 10^{10.3}Msun or M_halo < 10^{11.4}Msun), while the
conventional "hot mode" dominates the growth of high mass systems. Cold
accretion is often directed along filaments, allowing galaxies to efficiently
draw gas from large distances, while hot accretion is quasi-spherical. The
galaxy and halo mass dependence leads to redshift and environment dependence of
cold and hot accretion rates, with cold mode dominating at high redshift and in
low density regions today, and hot mode dominating in group and cluster
environments at low redshift. Star formation rates closely track accretion
rates, and we discuss the physics behind the observed environment and redshift
dependence of galactic scale star formation. If we allowed hot accretion to be
suppressed by conduction or AGN feedback, then the simulation predictions would
change in interesting ways, perhaps resolving conflicts with the colors of
ellipticals and the cutoff of the galaxy luminosity function. The transition
between cold and hot accretion at M_h ~ 10^{11.4}Msun is similar to that found
by Birnboim & Dekel (2003) using 1-d simulations and analytic arguments. The
corresponding baryonic mass is tantalizingly close to the scale at which
Kauffmann et al. (2003) find a marked shift in galaxy properties. We speculate
on connections between these theoretical and observational transitions.Comment: 1 figure added, Appendix discussing SAMs added, some text changes.
Matches the version accepted by MNRAS. 31 pages (MNRAS style), 21 figures,For
high resolution version of the paper (highly recommended) follow
http://www.astro.umass.edu/~keres/paper/ms2.ps.g
Accretion, feedback and galaxy bimodality: a comparison of the GalICS semi-analytic model and cosmological SPH simulations
We compare the galaxy population of an SPH simulation to those predicted by
the GalICS semi-analytic model and a stripped down version without supernova
and AGN feedback. The SPH simulation and the no-feedback GalICS model make
similar predictions for the baryonic mass functions of galaxies and for the
dependence of these mass functions on environment and redshift. The two methods
also make similar predictions for the galaxy content of dark matter haloes as a
function of halo mass and for the gas accretion history of galaxies. Both the
SPH and no-feedback GalICS models predict a bimodal galaxy population at z=0.
The "red'' sequence of gas poor, old galaxies is populated mainly by satellite
systems while, contrary to observations, the central galaxies of massive haloes
lie on the "blue'' star-forming sequence as a result of continuing hot gas
accretion at late times. Furthermore, both models overpredict the observed
baryonic mass function, especially at the high mass end. In the full GalICS
model, supernova-driven outflows reduce the masses of low and intermediate mass
galaxies by about a factor of two. AGN feedback suppresses gas cooling in large
haloes, producing a sharp cut-off in the baryonic mass function and moving the
central galaxies of these massive haloes to the red sequence. Our results imply
that the observational failings of the SPH simulation and the no-feedback
GalICS model are a consequence of missing input physics rather than
computational inaccuracies, that truncating gas accretion by satellite galaxies
automatically produces a bimodal galaxy distribution with a red sequence, but
that explaining the red colours of the most massive galaxies requires a
mechanism like AGN feedback that suppresses the accretion onto central galaxies
in large haloes.Comment: 17 pages, 11 figures, submitted to MNRA
Feedback first: the surprisingly weak effects of magnetic fields, viscosity, conduction, and metal diffusion on galaxy formation
Using high-resolution simulations with explicit treatment of stellar feedback
physics based on the FIRE (Feedback in Realistic Environments) project, we
study how galaxy formation and the interstellar medium (ISM) are affected by
magnetic fields, anisotropic Spitzer-Braginskii conduction and viscosity, and
sub-grid metal diffusion from unresolved turbulence. We consider controlled
simulations of isolated (non-cosmological) galaxies but also a limited set of
cosmological "zoom-in" simulations. Although simulations have shown significant
effects from these physics with weak or absent stellar feedback, the effects
are much weaker than those of stellar feedback when the latter is modeled
explicitly. The additional physics have no systematic effect on galactic star
formation rates (SFRs) . In contrast, removing stellar feedback leads to SFRs
being over-predicted by factors of . Without feedback, neither
galactic winds nor volume filling hot-phase gas exist, and discs tend to
runaway collapse to ultra-thin scale-heights with unphysically dense clumps
congregating at the galactic center. With stellar feedback, a multi-phase,
turbulent medium with galactic fountains and winds is established. At currently
achievable resolutions and for the investigated halo mass range
, the additional physics investigated here (MHD,
conduction, viscosity, metal diffusion) have only weak (-level)
effects on regulating SFR and altering the balance of phases, outflows, or the
energy in ISM turbulence, consistent with simple equipartition arguments. We
conclude that galactic star formation and the ISM are primarily governed by a
combination of turbulence, gravitational instabilities, and feedback. We add
the caveat that AGN feedback is not included in the present work
Quasi-Spherical Light Cones of the Kerr Geometry
Quasi-spherical light cones are lightlike hypersurfaces of the Kerr geometry
that are asymptotic to Minkowski light cones at infinity. We develop the
equations of these surfaces and examine their properties. In particular, we
show that they are free of caustics for all positive values of the Kerr radial
coordinate r. Useful applications include the propagation of high-frequency
waves, the definition of Kruskal-like coordinates for a spinning black hole and
the characteristic initial-value problem.Comment: LaTeX, 14 pages, 2 figure
A new population of recently quenched elliptical galaxies in the SDSS
We use the Sloan Digital Sky Survey to investigate the properties of massive
elliptical galaxies in the local Universe (z\leq0.08) that have unusually blue
optical colors. Through careful inspection, we distinguish elliptical from
non-elliptical morphologies among a large sample of similarly blue galaxies
with high central light concentrations (c_r\geq2.6). These blue ellipticals
comprise 3.7 per cent of all c_r\geq2.6 galaxies with stellar masses between
10^10 and 10^11 h^{-2} {\rm M}_{\sun}. Using published fiber spectra
diagnostics, we identify a unique subset of 172 non-star-forming ellipticals
with distinctly blue urz colors and young (< 3 Gyr) light-weighted stellar
ages. These recently quenched ellipticals (RQEs) have a number density of
2.7-4.7\times 10^{-5}\,h^3\,{\rm Mpc}^{-3} and sufficient numbers above
2.5\times10^{10} h^{-2} {\rm M}_{\sun} to account for more than half of the
expected quiescent growth at late cosmic time assuming this phase lasts 0.5
Gyr. RQEs have properties that are consistent with a recent merger origin
(i.e., they are strong `first-generation' elliptical candidates), yet few
involved a starburst strong enough to produce an E+A signature. The preferred
environment of RQEs (90 per cent reside at the centers of < 3\times
10^{12}\,h^{-1}{\rm M}_{\sun} groups) agrees well with the `small group scale'
predicted for maximally efficient spiral merging onto their halo center and
rules out satellite-specific quenching processes. The high incidence of Seyfert
and LINER activity in RQEs and their plausible descendents may heat the
atmospheres of small host halos sufficiently to maintain quenching.Comment: 26 pages, 9 figures. Revised version; accepted for publication in
MNRA
A Virtual Sky with Extragalactic HI and CO Lines for the SKA and ALMA
We present a sky simulation of the atomic HI emission line and the first ten
CO rotational emission lines of molecular gas in galaxies beyond the Milky Way.
The simulated sky field has a comoving diameter of 500/h Mpc, hence the actual
field-of-view depends on the (user-defined) maximal redshift zmax; e.g. for
zmax=10, the field of view yields ~4x4 sqdeg. For all galaxies, we estimate the
line fluxes, line profiles, and angular sizes of the HI and CO emission lines.
The galaxy sample is complete for galaxies with cold hydrogen masses above 10^8
Msun. This sky simulation builds on a semi-analytic model of the cosmic
evolution of galaxies in a Lambda-cold dark matter (LCDM) cosmology. The
evolving CDM-distribution was adopted from the Millennium Simulation, an N-body
CDM-simulation in a cubic box with a side length of 500/h Mpc. This side length
limits the coherence scale of our sky simulation: it is long enough to allow
the extraction of the baryon acoustic oscillations (BAOs) in the galaxy power
spectrum, yet the position and amplitude of the first acoustic peak will be
imperfectly defined. This sky simulation is a tangible aid to the design and
operation of future telescopes, such the SKA, the LMT, and ALMA. The results
presented in this paper have been restricted to a graphical representation of
the simulated sky and fundamental dN/dz-analyzes for peak flux density limited
and total flux limited surveys of HI and CO. A key prediction is that HI will
be harder to detect at redshifts z>2 than predicted by a no-evolution model.
The future verification or falsification of this prediction will allow us to
qualify the semi-analytic models.Comment: 16 pages, 9 figures, 1 tabl
Prediction of the Cosmic Evolution of the CO-Luminosity Functions
We predict the emission line luminosity functions (LFs) of the first 10
rotational transitions of CO in galaxies at redshift z=0 to z=10. This
prediction relies on a recently presented simulation of the molecular cold gas
content in ~3e7 evolving galaxies based on the Millennium Simulation. We
combine this simulation with a model for the conversion between molecular mass
and CO-line intensities, which incorporates the following mechanisms: (i)
molecular gas is heated by the CMB, starbursts (SBs), and active galactic
nuclei (AGNs); (ii) molecular clouds in dense or inclined galaxies can overlap;
(iii) compact gas can attain a smooth distribution in the densest part of
disks; (iv) CO-luminosities scale with metallicity changes between galaxies;
(v) CO-luminosities are always detected against the CMB. We analyze the
relative importance of these effects and predict the cosmic evolution of the
CO-LFs. The most notable conclusion is that the detection of regular galaxies
(i.e. no AGN, no massive SB) at high z>7 in CO-emission will be dramatically
hindered by the weak contrast against the CMB, in contradiction to earlier
claims that CMB-heating will ease the detection of high-redshift CO. The full
simulation of extragalactic CO-lines and the predicted CO-LFs at any redshift
can be accessed online, prior registration required} and they should be useful
for the modeling of CO-line surveys with future telescopes, such as ALMA, the
LMT, or the SKA.Comment: 8 figures, 1 tabl
The MOSFIRE Deep Evolution Field (MOSDEF) Survey: Rest-Frame Optical Spectroscopy for ~1500 H-Selected Galaxies at 1.37 < z < 3.8
In this paper we present the MOSFIRE Deep Evolution Field (MOSDEF) survey.
The MOSDEF survey aims to obtain moderate-resolution (R=3000-3650) rest-frame
optical spectra (~3700-7000 Angstrom) for ~1500 galaxies at 1.37<z<3.80 in
three well-studied CANDELS fields: AEGIS, COSMOS, and GOODS-N. Targets are
selected in three redshift intervals: 1.37<z<1.70, 2.09<z<2.61, and
2.95<z<3.80, down to fixed H_AB (F160W) magnitudes of 24.0, 24.5 and 25.0,
respectively, using the photometric and spectroscopic catalogs from the 3D-HST
survey. We target both strong nebular emission lines (e.g., [OII], Hbeta,
[OIII], 5008, Halpha, [NII], and [SII]) and stellar continuum and absorption
features (e.g., Balmer lines, Ca-II H and K, Mgb, 4000 Angstrom break). Here we
present an overview of our survey, the observational strategy, the data
reduction and analysis, and the sample characteristics based on spectra
obtained during the first 24 nights. To date, we have completed 21 masks,
obtaining spectra for 591 galaxies. For ~80% of the targets we derive a robust
redshift from either emission or absorption lines. In addition, we confirm 55
additional galaxies, which were serendipitously detected. The MOSDEF galaxy
sample includes unobscured star-forming, dusty star-forming, and quiescent
galaxies and spans a wide range in stellar mass (~10^9-10^11.5 Msol) and star
formation rate (~10^0-10^3 Msol/yr). The spectroscopically confirmed sample is
roughly representative of an H-band limited galaxy sample at these redshifts.
With its large sample size, broad diversity in galaxy properties, and wealth of
available ancillary data, MOSDEF will transform our understanding of the
stellar, gaseous, metal, dust, and black hole content of galaxies during the
time when the universe was most active.Comment: Accepted for publication in ApJS; 28 pages, 19 figures; MOSDEF
spectroscopic redshifts available at
http://mosdef.astro.berkeley.edu/Downloads.htm
Keck spectroscopy and Spitzer Space Telescope analysis of the outer disk of the Triangulum Spiral Galaxy M33
In an earlier study of the spiral galaxy M33, we photometrically identified
arcs or outer spiral arms of intermediate age (0.6 Gyr - 2 Gyr) carbon stars
precisely at the commencement of the HI-warp. Stars in the arcs were
unresolved, but were likely thermally-pulsing asymptotic giant branch carbon
stars. Here we present Keck I spectroscopy of seven intrinsically bright and
red target stars in the outer, northern arc in M33. The target stars have
estimated visual magnitudes as faint as V \sim 25 mag. Absorption bands of CN
are seen in all seven spectra reported here, confirming their carbon star
status. In addition, we present Keck II spectra of a small area 0.5 degree away
from the centre of M33; the target stars there are also identified as carbon
stars. We also study the non-stellar PAH dust morphology of M33 secured using
IRAC on board the Spitzer Space Telescope. The Spitzer 8 micron image attests
to a change of spiral phase at the start of the HI warp. The Keck spectra
confirm that carbon stars may safely be identified on the basis of their red
J-K_s colours in the outer, low metallicity disk of M33. We propose that the
enhanced number of carbon stars in the outer arms are an indicator of recent
star formation, fueled by gas accretion from the HI-warp reservoir.Comment: 9 pages, 5 figures, accepted in A&
IMAGES-III: The evolution of the Near-Infrared Tully-Fisher relation over the last 6 Gyr
Using the multi-integral field spectrograph GIRAFFE at VLT, we have derived
the K-band Tully-Fisher relation (TFR) at z~0.6 for a representative sample of
65 galaxies with emission lines. We confirm that the scatter in the z~0.6 TFR
is caused by galaxies with anomalous kinematics, and find a positive and strong
correlation between the complexity of the kinematics and the scatter that they
contribute to the TFR. Considering only relaxed-rotating disks, the scatter,
and possibly also the slope of the TFR, do not appear to evolve with z. We
detect an evolution of the K-band TFR zero point between z~0.6 and z=0, which,
if interpreted as an evolution of the K-band luminosity of rotating disks,
would imply that a brightening of 0.66+/-0.14 mag occurs between z~0.6 and z=0.
Any disagreement with the results of Flores et al. (2006) are attributed to
both an improvement of the local TFR and the more detailed accurate measurement
of the rotation velocities in the distant sample. Most of the uncertainty can
be explained by the relatively coarse spatial-resolution of the kinematical
data. Because most rotating disks at z~0.6 are unlikely to experience further
merging events, one may assume that their rotational velocity does not evolve
dramatically. If true, our result implies that rotating disks observed at z~0.6
are rapidly transforming their gas into stars, to be able to double their
stellar masses and be observed on the TFR at z=0. The rotating disks observed
are indeed emission-line galaxies that are either starbursts or LIRGs, which
implies that they are forming stars at a high rate. Thus, a significant
fraction of the rotating disks are forming the bulk of their stars within 6 to
8 Gyr, in good agreement with former studies of the evolution of the M-Z
relation.Comment: 17 pages, 11 figures, accepted for publication in A&A. v2 taking into
account comments from language edito