20 research outputs found
The stellar mass function and star formation rate-stellar mass relation of galaxies at z ~ 4 - 7
We investigate the evolution of the star formation rate-stellar mass relation
(SFR-M*) and Galaxy Stellar Mass Function (GSMF) of z ~ 4-7 galaxies, using
cosmological simulations run with the smoothed particle hydrodynamics code
P-GADGET3(XXL). We explore the effects of different feedback prescriptions
(supernova driven galactic winds and AGN feedback), initial stellar mass
functions and metal cooling. We show that our fiducial model, with strong
energy-driven winds and early AGN feedback, is able to reproduce the observed
stellar mass function obtained from Lyman-break selected samples of star
forming galaxies at redshift 6 < z < 7. At z ~ 4, observed estimates of the
GSMF vary according to how the sample was selected. Our simulations are more
consistent with recent results from K-selected samples, which provide a better
proxy of stellar masses and are more complete at the high mass end of the
distribution. We find that in some cases simulated and observed SFR-M*
relations are in tension, and this can lead to numerical predictions for the
GSMF in excess of the GSMF observed. By combining the simulated SFR(M*)
relationship with the observed star formation rate function at a given
redshift, we argue that this disagreement may be the result of the uncertainty
in the SFR-M* (Luv-M*) conversion. Our simulations predict a population of
faint galaxies not seen by current observations.Comment: 23 Pages, 13 figures, modified to match accepted version to MNRA
A Characteristic Mass Scale in the Mass-Metallicity Relation of Galaxies
We study the shape of the gas-phase mass-metallicity relation (MZR) of a
combined sample of present-day dwarf and high-mass star-forming galaxies using
IZI, a Bayesian formalism for measuring chemical abundances presented in Blanc
et al. 2015. We observe a characteristic stellar mass scale at M, above which the ISM undergoes a sharp increase in its
level of chemical enrichment. In the M range the MZR
follows a shallow power-law () with slope
. At approaching M the MZR
steepens significantly, showing a slope of in the
M range, and a flattening towards a constant
metallicity at higher stellar masses. This behavior is qualitatively different
from results in the literature that show a single power-law MZR towards the low
mass end. We thoroughly explore systematic uncertainties in our measurement,
and show that the shape of the MZR is not induced by sample selection, aperture
effects, a changing N/O abundance, the adopted methodology used to construct
the MZR, secondary dependencies on star formation activity, nor diffuse ionized
gas (DIG) contamination, but rather on differences in the method used to
measure abundances. High resolution hydrodynamical simulations can
qualitatively reproduce our result, and suggest a transition in the ability of
galaxies to retain their metals for stellar masses above this threshold. The
MZR characteristic mass scale also coincides with a transition in the scale
height and clumpiness of cold gas disks, and a typical gas fraction below which
the efficiency of star formation feedback for driving outflows is expected to
decrease sharply.Comment: 24 pages, 11 figures, 4 tables, accepted for publication in Ap
Modelling the mass accretion histories of dark matter haloes using a Gamma formalism
We present a physical model of the Mass Accretion Histories (MAH) of haloes
in concordance with the {\it observed} cosmic star formation rate density
(CSFRD). We model the MAHs of dark matter haloes using a Gamma ()
functional form: , where is the halo mass at
present time, is time, and are parameters we explore,
is the percentage of the mass of the halo at z = 0 with respect to the
final mass of the halo achieved at . We use the MAHs of haloes
obtained from cosmological simulations and analytical models to constrain our
model. can be described by a power-law (). Haloes with small masses have already on average attained most of
their final masses. The average of haloes in the Universe is $ >
0.95$ pointing to the direction that the cosmic MAH/CSFRD is saturated at our
era. The average parameter (the depletion rate of the available
dark matter for halo growth) is related to the dynamical timescales of haloes.
The parameter is a power-law index of and represents the early
growth a halo experiences before the expansion of the Universe starts to slow
it down. Finally, (the time that marks the co-evolution/growth of
galaxies and haloes after the Big Bang) is found to be 150-300 million years.Comment: 18 pages, 8 figures, Accepted at MNRA
DESI Legacy Imaging Surveys Data Release 9: Cosmological Constraints from Galaxy Clustering and Weak Lensing using the Minimal Bias Model
We present a tentative constraint on cosmological parameters and
from a joint analysis of galaxy clustering and galaxy-galaxy lensing
from DESI Legacy Imaging Surveys Data Release 9 (DR9), covering approximately
10000 square degrees and spanning the redshift range of 0.1 to 0.9. To study
the dependence of cosmological parameters on lens redshift, we divide lens
galaxies into seven approximately volume-limited samples, each with an equal
width in photometric redshift. To retrieve the intrinsic projected correlation
function from the lens samples, we employ a novel method
to account for redshift uncertainties. Additionally, we measured the
galaxy-galaxy lensing signal for each lens sample,
using source galaxies selected from the shear catalog by applying our
\texttt{Fourier\_Quad} pipeline to DR9 images. We model these observables
within the flat CDM framework, employing the minimal bias model. To
ensure the reliability of the minimal bias model, we apply conservative scale
cuts: and , for and
, respectively. Our findings suggest a mild tendency
that increases with lens redshift,
although this trend is only marginally significant. When we combine low
redshift samples, the value of is determined to be ,
consistent with the Planck results but significantly higher than the 3
2pt analysis by 2-5. Despite the fact that further refinements in
measurements and modeling could improve the accuracy of our results, the
consistency with standard values demonstrates the potential of our method for
more precise and accurate cosmology in the future.Comment: slightly different with the published versio
Detection of a possible superluminous supernova in the epoch of reionization
An interesting transient has been detected in one of our three Dark Energy
Camera deep fields. Observations of these deep fields take advantage of the
high red sensitivity of DECam on the Cerro Tololo Interamerican Observatory
Blanco telescope. The survey includes the Y band with rest wavelength 1430{\AA}
at z = 6. Survey fields (the Prime field 0555-6130, the 16hr field 1600-75 and
the SUDSS New Southern Field) are deeper in Y than other infrared surveys. They
are circumpolar, allowing all night to be used efficiently, exploiting the moon
tolerance of 1 micron observations to minimize conflict with the Dark Energy
Survey. As an i-band dropout (meaning that the flux decrement shortward of
Lyman alpha is in the i bandpass), the transient we report here is a supernova
candidate with z ~ 6, with a luminosity comparable to the brightest known
current epoch superluminous supernova (i.e., ~ 2 x 10^11 solar luminosities).Comment: Reference adde