1,188 research outputs found
Structure and dynamics of high-z galaxies
HST and integral-field spectroscopic observations of star-forming galaxies at cosmic noon provide a view on the spatial distribution of stars, gas and dust, and probe gaseous motions revealing the central gravitational potential and local feedback processes at play. In this paper, we review recent insights gained from such observations, with an emphasis on results obtained through near-infrared imaging spectroscopy. Their context and implications are documented more fully in a forthcoming review article by Förster Schreiber & Wuyts (in prep).</p
Star-Forming Galaxies at Cosmic Noon
Ever deeper and wider lookback surveys have led to a fairly robust outline of the cosmic star formation history, which culminated around z~2 -- a period often nicknamed "cosmic noon." Our knowledge about star-forming galaxies at these epochs has dramatically advanced from increasingly complete population censuses and detailed views of individual galaxies. We highlight some of the key observational insights that influenced our current understanding of galaxy evolution in the equilibrium growth picture: â scaling relations between galaxy properties are fairly well established among massive galaxies at least out to z~2, pointing to regulating mechanisms already acting on galaxy growth; â resolved views reveal that gravitational instabilities and efficient secular processes within the gas- and baryon-rich galaxies at z~2 play an important role in the early build-up of galactic structure; â ever more sensitive observations of kinematics at z~2 are probing the baryon and dark matter budget on galactic scales and the links between star-forming galaxies and their likely descendants; â towards higher masses, massive bulges, dense cores, and powerful AGN and AGN-driven outflows are more prevalent and likely play a role in quenching star formation. We outline emerging questions and exciting prospects for the next decade with upcoming instrumentation, including the James Webb Space Telescope and the next generation of Extremely Large Telescopes
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
Resolved views on early galaxy evolution
Resolved observations of star-forming galaxies at cosmic noon with the Hubble Space Telescope and large ground-based facilities provide a view on the spatial distribution of stars, gas and dust, and probe gaseous motions revealing the central gravitational potential and local feedback processes at play. In this paper, we review recent insights gained from such observations, with an emphasis on results obtained through optical/near-infrared imaging and imaging spectroscopy. Their context and implications are documented more fully in a forthcoming review article by Förster Schreiber & Wuyts (in prep)
Measurement of the Mass and Stellar Population Distribution in M82 with the LBT
We present a K-band spectroscopic study of the stellar and gas kinematics,
mass distribution, and stellar populations of the archetypical starburst galaxy
M82. Our results are based on a single spectrum at a position angle of 67.5
degrees through the K-band nucleus. We used the CO stellar absorption band head
at 2.29 {\mu}m (CO_2.29) to measure the rotation curve out to nearly 4 kpc
radius on both the eastern and western sides of the galaxy. Our data show that
the rotation curve is flat from 1 - 4 kpc. This stands in sharp contrast to
some previous studies, which have interpreted H I and CO emission-line
position-velocity diagrams as evidence for a declining rotation curve. The
kinematics of the Br\gamma, H_2, and He I emission lines are consistent with,
although characterized by slightly higher velocities than, the stellar
kinematics. We derived M82's mass distribution from our stellar kinematic
measurements and estimate its total dynamical mass is ~10^10 Msun. We measured
the equivalent width of CO_2.29 (W_2.29) as a function of distance from the
center of the galaxy to investigate the spatial extent of the red supergiant
(RSG) population. The variation in W_2.29 with radius clearly shows that RSGs
dominate the light inside 500 pc radius. M82's superwind is likely launched
from this region, where we estimate the enclosed mass is <= 2 x 10^9 Msun.Comment: 6 pages, 6 figures. Submitted to ApJ. For a brief video explaining
the key result of this paper, see http://www.youtube.com/user/OSUAstronom
Mid-IR FORCAST/SOFIA Observations of M82
We present 75"x75" size maps of M82 at 6.4 micron, 6.6 micron, 7.7 micron,
31.5 micron, and 37.1 micron with a resolution of ~4" that we have obtained
with the mid-IR camera FORCAST on SOFIA. We find strong emission from the inner
60" (~1kpc) along the major axis, with the main peak 5" west-southwest of the
nucleus and a secondary peak 4" east-northeast of the nucleus. The detailed
morphology of the emission differs among the bands, which is likely due to
different dust components dominating the continuum emission at short mid-IR
wavelengths and long mid-IR wavelengths. We include Spitzer-IRS and
Herschel/PACS 70 micron data to fit spectral energy distribution templates at
both emission peaks. The best fitting templates have extinctions of A_V = 18
and A_V = 9 toward the main and secondary emission peak and we estimated a
color temperature of 68 K at both peaks from the 31 micron and 37 micron
measurement. At the emission peaks the estimated dust masses are on the order
of 10^{4} M_sun.Comment: ApJL in press (ApJ, 749, L19), article also available at at
http://stacks.iop.org/2041-8205/749/L1
Star formation in the CDFS: observations confront simulations
We investigate the star formation history of the universe using FIREWORKS, a
multiwavelength survey of the CDFS. We study the evolution of the specific star
formation rate (sSFR) with redshift in different mass bins from z = 0 to z ~ 3.
We find that the sSFR increases with redshift for all masses. The logarithmic
increase of the sSFR with redshift is nearly independent of mass, but this
cannot yet be verified at the lowest-mass bins at z > 0.8, due to
incompleteness. We convert the sSFRs to a dimensionless growth rate to
facilitate a comparison with a semi-analytic galaxy formation model that was
implemented on the Millennium Simulation. The model predicts that the growth
rates and sSFRs increase similarly with redshift for all masses, consistent
with the observations. However, we find that for all masses, the inferred
observed growth rates increase more rapidly with redshift than the model
predictions. We discuss several possible causes for this discrepancy, ranging
from field-to-field variance, conversions to SFR, and shape of the IMF. We find
that none of these can solve the discrepancy completely. We conclude that the
models need to be adapted to produce the steep increase in growth rate between
redshift z=0 and z=1.Comment: 7 pages, 5 figure
Spatially Resolved Star Formation History Along the Disk of M82 Using Multi-Band Photometric Data
We present the results on the star formation history and extinction in the
disk of M82 over spatial scales of 10" (~180 pc). Multi-band photometric data
covering from the far ultraviolet to the near infrared bands were fitted to a
grid of synthetic spectral energy distributions. We obtained distribution
functions of age and extinction for each of the 117 apertures analyzed, taking
into account observational errors through Monte-Carlo simulations. These
distribution functions were fitted with gaussian functions to obtain the mean
ages and extinctions along with errors on them. The analyzed zones include the
high surface brightness complexes defined by O'Connell & Mangano (1978). We
found that these complexes share the same star formation history and extinction
as the field stellar populations in the disk. There is an indication that the
stellar populations are marginally older at the outer disk (450 Myr at ~3 kpc)
as compared to the inner disk (100 Myr at 0.5 kpc). For the nuclear regions
(radius less than 500 pc), we obtained an age of less than 10 Myr. The results
obtained in this work are consistent with the idea that the 0.5-3 kpc part of
the disk of M82 formed around 90% of the stellar mass in a star-forming episode
that started around 450 Myr ago lasting for about 350 Myr. We found that field
stars are the major contributors to the flux over the spatial scales analyzed
in this study, with stellar cluster contribution being 7% in the nucleus and
0.7% in the disk.Comment: 19 pages, 14 figures. Accepted for publication in The Astrophysical
Journa
The Gemini spectral library of near-IR late type stellar templates and its application for velocity dispersion measurements
We present a spectroscopic library of late spectral type stellar templates in
the near-IR range 2.15-2.42microns, at R=5300-5900 resolution, oriented to
support stellar kinematics studies in external galaxies, such as the direct
determination of the masses of supermassive black-holes in nearby active (or
non-active) galaxies. The combination of high spectral resolution and
state-of-the-art instrumentation available in 8-m class telescopes has made the
analysis of circumnuclear stellar kinematics using the near-IR CO band heads
one of the most used techniques for such studies, and this library aims to
provide the supporting datasets required by the higher spectral resolution and
larger spectral coverage currently achieved with modern near-IR spectrographs.
Examples of the application for kinematical analysis are given for data
obtained with two Gemini instruments, but the templates can be easily adjusted
for use with other near-IR spectrographs at similar or lower resolution. The
example datasets are also used to revisit the "template mismatch" effect and
the dependence of the velocity dispersion values obtained from the fitting
process with the characteristics of the stellar templates. The library is
available in electronic form from the Gemini web pages (link above).Comment: To appear in the ApJ Supplement Series, December 2009. AASTex, 25
pages, 17 figures. The library spectra are available in standard FITS format
from the Gemini Observatory webpage at
http://www.gemini.edu/sciops/instruments/nearir-resources/?q=node/1016
Spatially resolved Halpha maps and sizes of 57 strongly star-forming galaxies at z~1 from 3D-HST: evidence for rapid inside-out assembly of disk galaxies
We investigate the build-up of galaxies at z~1 using maps of Halpha and
stellar continuum emission for a sample of 57 galaxies with rest-frame Halpha
equivalent widths >100 Angstroms in the 3D-HST grism survey. We find that the
Halpha emission broadly follows the rest-frame R-band light but that it is
typically somewhat more extended and clumpy. We quantify the spatial
distribution with the half-light radius. The median Halpha effective radius
r_e(Halpha) is 4.2+-0.1 kpc but the sizes span a large range, from compact
objects with r_e(Halpha) ~ 1.0 kpc to extended disks with r_e(Halpha) ~ 15 kpc.
Comparing Halpha sizes to continuum sizes, we find
=1.3+-0.1 for the full sample. That is, star formation, as
traced by Halpha, typically occurs out to larger radii than the rest-frame
R-band stellar continuum; galaxies are growing their radii and building up from
the inside out. This effect appears to be somewhat more pronounced for the
largest galaxies. Using the measured Halpha sizes, we derive star formation
rate surface densities. We find that they range from ~0.05 Msun yr^{-1}
kpc^{-2} for the largest galaxies to ~5 Msun yr^{-1} kpc^{-2} for the smallest
galaxies, implying a large range in physical conditions in rapidly star-forming
z~1 galaxies. Finally, we infer that all galaxies in the sample have very high
gas mass fractions and stellar mass doubling times < 500 Myr. Although other
explanations are also possible, a straightforward interpretation is that we are
simultaneously witnessing the rapid formation of compact bulges and large disks
at z~1.Comment: ApJ Letters, in press. The public 3D-HST website is
http://3dhst.research.yale.edu/Home.htm
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