1,726 research outputs found
Brief of Amicus Curiae National Center for Lesbian Rights, Fred T. Korematsu Center for Law and Equality, and Prof. Julie Shapiro
In re Marriage of Blac
The Presence of Weak Active Galactic Nuclei in High Redshift Star Forming Galaxies
We present [OIII 5007A] observations of the star forming galaxy HDF-BMZ1299
(z=1.598) using Keck Observatory's Adaptive Optics system with the
near-infrared integral field spectrograph OSIRIS. Using previous Halpha and
[NII] measurements of the same source, we are able for the first time to use
spatially resolved observations to place a high-redshift galaxy's substructure
on a traditional HII diagnostic diagram. We find that HDF-BMZ1299's spatially
concentrated nebular ratios in the central ~1.5 kiloparsec (0."2) are best
explained by the presence of an AGN: log([NII]/Halpha)=-0.22+/-0.05 and 2sigma
limit of log([OIII]/Hbeta)>0.26. The dominant energy source of this galaxy is
star formation, and integrating a single aperture across the galaxy yields
nebular ratios that are composite spectra from both AGN and HII regions. The
presence of an embedded AGN in HDF-BMZ1299 may suggest a potential
contamination in a fraction of other high-redshift star forming galaxies, and
we suggest that this may be a source of the "elevated" nebular ratios
previously seen in seeing-limited metallicity studies. HDF-BMZ1299's estimated
AGN luminosity is L_Halpha = 3.7e41 erg/s and L_[OIII] = 5.8e41 erg/s, making
it one of the lowest luminosity AGN discovered at this early epoch.Comment: 15 pages, 4 figures, ApJ Accepted, new version to be published
(updated text, figures, and table
The Impact of cold gas accretion above a mass floor on galaxy scaling relations
Using the cosmological baryonic accretion rate and normal star formation
efficiencies, we present a very simple model for star-forming galaxies (SFGs)
that accounts for the mass and redshift dependencies of the SFR-Mass and
Tully-Fisher relations from z=2 to the present. The time evolution follows from
the fact that each modelled galaxy approaches a steady state where the SFR
follows the (net) cold gas accretion rate. The key feature of the model is a
halo mass floor M_{min}~10^{11} below which accretion is quenched in order to
simultaneously account for the observed slopes of the SFR-Mass and
Tully-Fischer relations. The same successes cannot be achieved via a
star-formation threshold (or delay) nor by varying the SF efficiency or the
feedback efficiency. Combined with the mass ceiling for cold accretion due to
virial shock heating, the mass floor M_{min} explains galaxy "downsizing",
where more massive galaxies formed earlier and over a shorter period of time.
It turns out that the model also accounts for the observed galactic baryon and
gas fractions as a function of mass and time, and the cosmic SFR density from
z~6 to z=0, which are all resulting from the mass floor M_{min}. The model
helps to understand that it is the cosmological decline of accretion rate that
drives the decrease of cosmic SFR density between z~2 and z=0 and the rise of
the cosmic SFR density allows us to put a constraint on our main parameter
M_{min}~10^{11} solar masses. Among the physical mechanisms that could be
responsible for the mass floor, we view that photo-ionization feedback (from
first in-situ hot stars) lowering the cooling efficiency is likely to play a
large role.Comment: 19pages, 14 figures, accepted to ApJ, updated reference
The Kiloparsec-Scale Kinematics of High-Redshift Star-Forming Galaxies
We present the results of a spectroscopic survey of the kinematic structure
of star-forming galaxies at redshift z ~ 2 - 3 using Keck/OSIRIS integral field
spectroscopy. Our sample is comprised of 12 galaxies between redshifts z ~ 2.0
and 2.5 and one galaxy at z ~ 3.3 which are well detected in either HAlpha or
[O III] emission. These observations were obtained in conjunction with the Keck
laser guide star adaptive optics system, with a typical angular resolution
after spatial smoothing ~ 0.15" (approximately 1 kpc at the redshift of the
target sample). At most five of these 13 galaxies have spatially resolved
velocity gradients consistent with rotation while the remaining galaxies have
relatively featureless or irregular velocity fields. All of our galaxies show
local velocity dispersions ~ 60 - 100 km/s, suggesting that (particularly for
those galaxies with featureless velocity fields) rotation about a preferred
axis may not be the dominant mechanism of physical support. While some galaxies
show evidence for major mergers such evidence is unrelated to the kinematics of
individual components (one of our strongest merger candidates also exhibits
unambiguous rotational structure), refuting a simple bimodal disk/merger
classification scheme. We discuss these data in light of complementary surveys
and extant UV-IR spectroscopy and photometry, concluding that the dynamical
importance of cold gas may be the primary factor governing the observed
kinematics of z ~ 2 galaxies. We conclude by speculating on the importance of
mechanisms for accreting low angular-momentum gas and the early formation of
quasi-spheroidal systems in the young universe.(abridged)Comment: 34 pages, 13 figures. Revised version accepted for publication in the
Astrophysical Journal. Version with full-resolution figures is available at
http://www.astro.ucla.edu/~drlaw/Papers/OSIRIS_data2.pd
The SINS/zC-SINF survey of z~2 galaxy kinematics: Outflow properties
Based on SINFONI Ha, [NII] and [SII] AO data of 30 z \sim 2 star-forming
galaxies (SFGs) from the SINS and zcSINF surveys, we find a strong correlation
of the Ha broad flux fraction with the star formation surface density of the
galaxy, with an apparent threshold for strong outflows occurring at 1 Msun
yr^-1 kpc^-2. Above this threshold, we find that SFGs with logm_\ast>10 have
similar or perhaps greater wind mass loading factors (eta = Mdotout/SFR) and
faster outflow velocities than lower mass SFGs. This trend suggests that the
majority of outflowing gas at z \sim 2 may derive from high-mass SFGs, and that
the z \sim 2 mass-metallicity relation is driven more by dilution of enriched
gas in the galaxy gas reservoir than by the efficiency of outflows. The mass
loading factor is also correlated with the SFR and inclination, such that more
star-forming and face-on galaxies launch more powerful outflows. For galaxies
that have evidence for strong outflows, we find that the broad emission is
spatially extended to at least the half-light radius (\sim a few kpc). We
propose that the observed threshold for strong outflows and the observed mass
loading of these winds can be explained by a simple model wherein break-out of
winds is governed by pressure balance in the disk. Using the ratio of the [SII]
doublet in a broad and narrow component, we find that outflowing gas has a
density of \sim10-100 cm^-3, significantly less than that of the star forming
gas (600 cm^-3).Comment: 7 pages, 3 figures, accepted by Ap
Constraints on the assembly and dynamics of galaxies. II. Properties of kiloparsec-scale clumps in rest-frame optical emission of z ~ 2 star-forming galaxies
We study the properties of luminous stellar clumps identified in deep, high
resolution HST/NIC2 F160W imaging at 1.6um of six z~2 star-forming galaxies
with existing near-IR integral field spectroscopy from SINFONI at the VLT.
Individual clumps contribute ~0.5%-15% of the galaxy-integrated rest-frame
~5000A emission, with median of about 2%; the total contribution of clump light
ranges from 10%-25%. The median intrinsic clump size and stellar mass are ~1kpc
and log(Mstar[Msun])~9, in the ranges for clumps identified in rest-UV or line
emission in other studies. The clump sizes and masses in the subset of disks
are broadly consistent with expectations for clump formation via gravitational
instabilities in gas-rich, turbulent disks given the host galaxies' global
properties. By combining the NIC2 data with ACS/F814W imaging available for one
source, and AO-assisted SINFONI Halpha data for another, we infer modest color,
M/L, and stellar age variations within each galaxy. In these two objects, sets
of clumps identified at different wavelengths do not fully overlap;
NIC2-identified clumps tend to be redder/older than ACS- or Halpha-identified
clumps without rest-frame optical counterparts. There is evidence for a
systematic trend of older ages at smaller galactocentric radii among the
clumps, consistent with scenarios where inward migration of clumps transports
material towards the central regions. From constraints on a bulge-like
component at radii <1-3kpc, none of the five disks in our sample appears to
contain a compact massive stellar core, and we do not discern a trend of bulge
stellar mass fraction with stellar age of the galaxy. Further observations are
necessary to probe the build-up of stellar bulges and the role of clumps in
this process.Comment: 29 pages, 11 figures. Revised version accepted for publication in the
Astrophysical Journa
High-Redshift Star-Forming Galaxies: Angular Momentum and Baryon Fraction, Turbulent Pressure Effects and the Origin of Turbulence
The structure of a sample of high-redshift (z=2), rotating galaxies with high
star formation rates and turbulent gas velocities of sigma=40-80 km/s is
investigated. Fitting the observed disk rotational velocities and radii with a
Mo, Mao, White (1998) (MMW) model requires unusually large disk spin parameters
lambda_d>0.1 and disk-to-dark halo mass fraction m_d=0.2, close to the cosmic
baryon fraction. The galaxies segregate into dispersion-dominated systems with
1<vmax/sigma<3, maximum rotational velocities vmax<200 km/s and disk half-light
radii rd=1-3 kpc and rotation-dominated systems with vmax>200 km/s,
vmax/sigma>3 and rd=4-8 kpc. For the dispersion-dominated sample, radial
pressure gradients partly compensate the gravitational force, reducing the
rotational velocities. Including this pressure effect in the MMW model,
dispersion-dominated galaxies can be fitted well with spin parameters lf
lambda_d=0.03-0.05 for high disk mass fractions of m_d=0.2 and with
lambda_d=0.01-0.03 for m_d=0.05. These values are in good agreement with
cosmological expectations. For the rotation-dominated sample however pressure
effects are small and better agreement with theoretically expected disk spin
parameters can only be achieved if the dark halo mass contribution in the
visible disk regime (2-3*rd) is smaller than predicted by the MMW model. We
argue that these galaxies can still be embedded in standard cold dark matter
halos if the halos did not contract adiabatically in response to disk
formation. It is shown that the observed high turbulent gas motions of the
galaxies are consistent with a Toomre instability parameter Q=1 which is equal
to the critical value, expected for gravitational disk instability to be the
major driver of turbulence. The dominant energy source of turbulence is then
the potential energy of the gas in the disk.Comment: 23 pages, 4 figures, ApJ, in pres
2D Kinematics and Physical Properties of z~3 Star-Forming Galaxies
We present results from a study of the kinematic structure of star-forming
galaxies at redshift z~3 selected in the VVDS, using integral-field
spectroscopy of rest-frame optical nebular emission lines, in combination with
rest-frame UV spectroscopy, ground-based optical/near-IR and Spitzer
photometry. We also constrain the underlying stellar populations to address the
evolutionary status of these galaxies. We infer the kinematic properties of
four galaxies: VVDS-20298666, VVDS-020297772, VVDS-20463884 and VVDS-20335183
with redshifts z = 3.2917, 3.2878, 3.2776, and 3.7062, respectively. While
VVDS-20463884 presents an irregular velocity field with a peak in the local
velocity dispersion of the galaxy shifted from the centre of the galaxy,
VVDS-20298666 has a well-resolved gradient in velocity over a distance of ~4.5
kpc with a peak-to-peak amplitude of v = 91 km/s . We discovered that the
nearby galaxy, VVDS-020297772 (which shows traces of AGN activity), is in fact
a companion at a similar redshift with a projected separated of 12 kpc. In
contrast, the velocity field of VVDS-020335183 seems more consistent with a
merger on a rotating disk. However, all of the objects have a high local
velocity dispersion (sigma ~ 60-70 km/s), which gives v/sigma < 1. It is
unlikely that these galaxies are dynamically cold rotating disk of ionized gas.Comment: 14 pages and 16 figure
Short-lived star-forming giant clumps in cosmological simulations of z~2 disks
Many observed massive star-forming z\approx2 galaxies are large disks that
exhibit irregular morphologies, with \sim1kpc, \sim10^(8-10)Msun clumps. We
present the largest sample to date of high-resolution cosmological SPH
simulations that zoom-in on the formation of individual M*\sim10^(10.5)Msun
galaxies in \sim10^(12)Msun halos at z\approx2. Our code includes strong
stellar feedback parameterized as momentum-driven galactic winds. This model
reproduces many characteristic features of this observed class of galaxies,
such as their clumpy morphologies, smooth and monotonic velocity gradients,
high gas fractions (f_g\sim50%) and high specific star-formation rates
(\gtrsim1Gyr^(-1)). In accord with recent models, giant clumps
(Mclump\sim(5x10^8-10^9)Msun) form in-situ via gravitational instabilities.
However, the galactic winds are critical for their subsequent evolution. The
giant clumps we obtain are short-lived and are disrupted by wind-driven mass
loss. They do not virialise or migrate to the galaxy centers as suggested in
recent work neglecting strong winds. By phenomenologically implementing the
winds that are observed from high-redshift galaxies and in particular from
individual clumps, our simulations reproduce well new observational constraints
on clump kinematics and clump ages. In particular, the observation that older
clumps appear closer to their galaxy centers is reproduced in our simulations,
as a result of inside-out formation of the disks rather than inward clump
migration.Comment: 11 pages, 6 figures, 1 table. Accepted for publication in the
Astrophysical Journa
Morphologies of local Lyman break galaxy analogs II: A Comparison with galaxies at z=2-4 in ACS and WFC3 images of the Hubble Ultra Deep Field
Lyman break galaxies (LBGs) display a range in structures (from
single/compact to clumpy/extended) that is different from typical local
star-forming galaxies. Recently, we have introduced a sample of rare, nearby
(z<0.3) starbursts that appear to be good analogs of LBGs. These "Lyman Break
Analogs" (LBAs) provide an excellent training set for understanding starbursts
at different redshifts. We present an application of this by comparing the
rest-frame UV/optical morphologies of 30 LBAs with those of sBzK galaxies at
z~2, and LBGs at z~3-4 in the HUDF. The UV/optical colors and sizes of LBAs and
LBGs are very similar, while the BzK galaxies are somewhat redder and larger.
There is significant overlap between the morphologies (G, C, A and M_20) of the
local and high-z samples, although the latter are somewhat less concentrated
and clumpier. We find that in the majority of LBAs the starbursts appear to be
triggered by interactions/mergers. When the images of the LBAs are degraded to
the same sensitivity and resolution as the images of LBGs and BzK galaxies,
these relatively faint asymmetric features are no longer detectable. This
effect is particularly severe in the rest-frame UV. It has been suggested that
high-z galaxies experience intense bursts unlike anything seen locally,
possibly due to cold flows and instabilities. In part, this is based on the
fact that the majority (~70%) of LBGs do not show morphological signatures of
mergers. Our results suggest that this evidence is insufficient, since a large
fraction of such signatures would likely have been missed in current
observations of z>2 galaxies. This leaves open the possibility that clumpy
accretion and mergers remain important in driving the evolution of these
starbursts, together with rapid gas accretion through other means.Comment: ApJ, In Press (14 pages, 7 figures; minor changes since v1). For
background material, see http://www.mpa-garching.mpg.de/~overzier/index.htm
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