115 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
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)
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
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
Structure and star formation in galaxies out to z=3: evidence for surface density dependent evolution and upsizing
We present an analysis of galaxies in the CDF-South. We find a tight relation
to z=3 between color and size at a given mass, with red galaxies being small,
and blue galaxies being large. We show that the relation is driven by stellar
surface density or inferred velocity dispersion: galaxies with high surface
density are red and have low specific star formation rates, and galaxies with
low surface density are blue and have high specific star formation rates.
Surface density and inferred velocity dispersion are better correlated with
specific star formation rate and color than stellar mass. Hence stellar mass by
itself is not a good predictor of the star formation history of galaxies. In
general, galaxies at a given surface density have higher specific star
formation rates at higher redshift. Specifically, galaxies with a surface
density of 1-3 10^9 Msun/kpc^2 are "red and dead" at low redshift,
approximately 50% are forming stars at z=1, and almost all are forming stars by
z=2. This provides direct additional evidence for the late evolution of
galaxies onto the red sequence. The sizes of galaxies at a given mass evolve
like 1/(1+z)^(0.59 +- 0.10). Hence galaxies undergo significant upsizing in
their history. The size evolution is fastest for the highest mass galaxies, and
quiescent galaxies. The persistence of the structural relations from z=0 to
z=2.5, and the upsizing of galaxies imply that a relation analogous to the
Hubble sequence exists out to z=2.5, and possibly beyond. The star forming
galaxies at z >= 1.5 are quite different from star forming galaxies at z=0, as
they have likely very high gas fractions, and star formation time scales
comparable to the orbital time.Comment: 20 pages, accepted for publication in ApJ, 2008, 68
Incidence, scaling relations and physical conditions of ionized gas outflows in MaNGA
In this work, we investigate the strength and impact of ionised gas outflows
within MaNGA galaxies. We find evidence for outflows in 322
galaxies ( of the analysed line-emitting sample), 185 of which show
evidence for AGN activity. Most outflows are centrally concentrated with a
spatial extent that scales sublinearly with . The incidence of
outflows is enhanced at higher masses, central surface densities and deeper
gravitational potentials, as well as at higher SFR and AGN luminosity. We
quantify strong correlations between mass outflow rates and the mechanical
drivers of the outflow of the form
and . We derive a master scaling
relation describing the mass outflow rate of ionised gas as a function of
, SFR, and . Most of the observed winds are
anticipated to act as galactic fountains, with the fraction of galaxies with
escaping winds increasing with decreasing potential well depth. We further
investigate the physical properties of the outflowing gas finding evidence for
enhanced attenuation in the outflow, possibly due to metal-enriched winds, and
higher excitation compared to the gas in the galactic disk. Given that the
majority of previous studies have focused on more extreme systems with higher
SFRs and/or more luminous AGN, our study provides a unique view of the
non-gravitational gaseous motions within `typical' galaxies in the low-redshift
Universe, where low-luminosity AGN and star formation contribute jointly to the
observed outflow phenomenology.Comment: Accepted for publication in MNRAS, 27 pages, Fig 7 & 8 for scaling
wind strength with drivers, Fig 10 for master scalin
Cool outflows in MaNGA:a systematic study and comparison to the warm phase
This paper investigates the neutral gas phase of galactic winds via the Na I
D{\AA} feature within MaNGA galaxies,
and directly compares their incidence and strength to the ionized winds
detected within the same parent sample. We find evidence for neutral outflows
in 127 galaxies ( per cent of the analysed line-emitting sample). Na I
D winds are preferentially seen in galaxies with dustier central regions and
both wind phases are more often found in systems with elevated SFR surface
densities, especially when there has been a recent upturn in the star formation
activity according to the SFR/SFR parameter. We find the
ionized outflow kinematics to be in line with what we measure in the neutral
phase. This demonstrates that, despite their small contributions to the total
outflow mass budget, there is value to collecting empirical measurements of the
ionized wind phase to provide information on the bulk motion in the outflow.
Depending on dust corrections applied to the ionized gas diagnostics, the
neutral phase has dex higher mass outflow rates
(), on average, compared to the ionized phase. We quantify
scaling relations between and the strengths of the physical
wind drivers (SFR, ). Using a radial-azimuthal stacking method, and by
considering inclination dependencies, we find results consistent with biconical
outflows orthogonal to the disk plane. Our work complements other multi-phase
outflow studies in the literature which consider smaller samples, more extreme
objects, or proceed via stacking of larger samples.Comment: This is a pre-copyedited, author-produced PDF of an article accepted
for publication in Monthly Notices of the Royal Astronomical Society (MNRAS)
following peer revie
Mergers and Mass Accretion Rates in Galaxy Assembly: The Millennium Simulation Compared to Observations of z~2 Galaxies
Recent observations of UV-/optically selected, massive star forming galaxies
at z~2 indicate that the baryonic mass assembly and star formation history is
dominated by continuous rapid accretion of gas and internal secular evolution,
rather than by major mergers. We use the Millennium Simulation to build new
halo merger trees, and extract halo merger fractions and mass accretion rates.
We find that even for halos not undergoing major mergers the mass accretion
rates are plausibly sufficient to account for the high star formation rates
observed in z~2 disks. On the other hand, the fraction of major mergers in the
Millennium Simulation is sufficient to account for the number counts of
submillimeter galaxies (SMGs), in support of observational evidence that these
are major mergers. When following the fate of these two populations in the
Millennium Simulation to z=0, we find that subsequent mergers are not frequent
enough to convert all z~2 turbulent disks into elliptical galaxies at z=0.
Similarly, mergers cannot transform the compact SMGs/red sequence galaxies at
z~2 into observed massive cluster ellipticals at z=0. We argue therefore, that
secular and internal evolution must play an important role in the evolution of
a significant fraction of z~2 UV-/optically and submillimeter selected galaxy
populations.Comment: 5 pages, 4 figures, Accepted for publication in Ap
Star-Forming Galaxies at z~2 and the Formation of the Metal-Rich Globular Cluster Population
We examine whether the super star-forming clumps (R~1-3 kpc; M~10^8-10^9.5
Msun) now known to be a key component of star-forming galaxies at z~2 could be
the formation sites of the locally observed old globular cluster population. We
find that the stellar populations of these super star-forming clumps are
excellent matches to those of local metal-rich globular clusters. Moreover,
this globular cluster population is known to be associated with the bulges /
thick disks of galaxies, and we show that its spatial distribution and
kinematics are consistent with the current understanding of the assembly of
bulges and thick disks from super star-forming clumps at high redshift.
Finally, with the assumption that star formation in these clumps proceeds as a
scaled-up version of local star formation in molecular clouds, this formation
scenario reproduces the observed numbers and mass spectra of metal-rich
globular clusters. The resulting link between the turbulent and clumpy disks
observed in high-redshift galaxies and a local globular cluster population
provides a plausible co-evolutionary scenario for several of the major
components of a galaxy: the bulge, the thick disk, and one of the globular
cluster populations.Comment: Accepted for publication in MNRAS Letters. 5 pages, 2 figure
Ultradeep Near-Infrared ISAAC Observations of the HDF-S: Observations, Reduction, Multicolor Catalog, and Photometric Redshifts
We present deep near-infrared (NIR) Js, H, and Ks-band ISAAC imaging of the
WFPC2 field of the HDF-S. The 2.5'x 2.5' high Galactic latitude field was
observed with the VLT under the best seeing conditions with integration times
amounting to 33.6 hours in Js, 32.3 hours in H, and 35.6 hours in Ks. We reach
total AB magnitudes for point sources of 26.8, 26.2, and 26.2 respectively (3
sigma), which make it the deepest ground-based NIR observations to date, and
the deepest Ks-band data in any field. The effective seeing of the coadded
images is ~0.45" in Js, ~0.48" in H, and ~0.46" in Ks. Using published WFPC2
optical data, we constructed a Ks-limited multicolor catalog containing 833
sources down to Ks,tot ~< 26 (AB), of which 624 have seven-band optical-to-NIR
photometry. These data allow us to select normal galaxies from their rest-frame
optical properties to high redshift (z ~< 4). The observations, data reduction
and properties of the final images are discussed, and we address the detection
and photometry procedures that were used in making the catalog. In addition, we
present deep number counts, color distributions and photometric redshifts of
the HDF-S galaxies. We find that our faint Ks-band number counts are flatter
than published counts in other deep fields, which might reflect cosmic
variations or different analysis techniques. Compared to the HDF-N, we find
many galaxies with very red V-H colors at photometric redshifts 1.95 < z < 3.5.
These galaxies are bright in Ks with infrared colors redder than Js-Ks > 2.3
(in Johnson magnitudes). Because they are extremely faint in the observed
optical, they would be missed by ultraviolet-optical selection techniques, such
as the U-dropout method.Comment: LaTeX, 24 pages, 15 figures, 3 tables. Accepted for publication in
the Astronomical Journal. The paper with full resolution images and figures
is available at http://www.strw.leidenuniv.nl/~fires/papers/2002Labbe.ps.gz .
The reduced data and catalogs can be found at
http://www.strw.leidenuniv.nl/~fires/data/hdfs
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