24 research outputs found
Galaxy Ecosystems: gas contents, inflows and outflows
We use a set of observational data for galaxy cold gas mass fraction and gas
phase metallicity to constrain the content, inflow and outflow of gas in
central galaxies hosted by halos with masses between to
. The gas contents in high redshift galaxies are obtained by
combining the empirical star formation histories of Lu et al. (2014) and star
formation models that relate star formation rate with the cold gas mass in
galaxies. We find that the total baryon mass in low-mass galaxies is always
much less than the universal baryon mass fraction since , regardless of
star formation model adopted. The data for the evolution of the gas phase
metallicity require net metal outflow at , and the metal loading
factor is constrained to be about , or about of the metal yield.
Based on the assumption that galactic outflow is more enriched in metal than
both the interstellar medium and the material ejected at earlier epochs, we are
able to put stringent constraints on the upper limits for both the net
accretion rate and the net mass outflow rate. The upper limits strongly suggest
that the evolution of the gas phase metallicity and gas mass fraction for
low-mass galaxies at is not compatible with strong outflow. We
speculate that the low star formation efficiency of low-mass galaxies is owing
to some preventative processes that prevent gas from accreting into galaxies in
the first place.Comment: 15 pages, 10 figures, submitted to MNRA
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An empirical approach to understanding of star formation in dark matter halos
We present a data-driven approach to understand the star formation in dark matter halos over cosmic time. With a simple empirical model and advanced tools for Bayesian inference, we try to constrain how galaxies have assembled their stars across cosmic time using stellar mass functions (SMFs) and the luminosity function of cluster galaxies. The key ingredients of the empirical model include dark halo merger trees and a generic function that links star formation rate (SFR) to the host halos. We found a new characteristic redshift zc ~ 2 above which the SFR in low mass halos \u3c 1011 solar mass must be enhanced relative to that at lower z. This leads to some interesting predictions, for instance, a signicant old stellar population in present-day dwarf galaxies with mass of 108 solar mass and steep low-mass end slopes of high redshift SMFs. The constrained empirical model can be combined with other other observational constraints to infer the physics behind the evolution of galaxies. The classical bulge mass could be derived from the major mergers of the host galaxies. Applying the central black hole (BHs) - classical bulge relation, it predicts all galaxies with stellar mass less than 1010.5 solar mass host intermediate mass BHs (MBH \u3c 107solar mass). Using the gas phase metallicity we study the evolution of gas and metal content of star forming galaxies and the infow and outfow rates. About 60% of the metals produced have been lost. At low redshift (z \u3c 1) the accretion of pristine gas should be lower by a factor of few than expected and the loading factor of gas outfow that is not recycled is of order of unity. The empirical model also serves as basis to study the evolution of satellite galaxies. The progenitors of present-day satellites can be initialized using this empirical model. The physically motivated models of quenching of star formation in satellites, including strangulation, ram pressure stripping of cold gas disks, and tidally triggered starburst, are tested against statistics of the group catalogs
Bayesian inferences of galaxy formation from the K-band luminosity and HI mass functions of galaxies: constraining star formation and feedback
We infer mechanisms of galaxy formation for a broad family of semi-analytic
models (SAMs) constrained by the K-band luminosity function and HI mass
function of local galaxies using tools of Bayesian analysis. Even with a broad
search in parameter space the whole model family fails to match to constraining
data. In the best fitting models, the star formation and feedback parameters in
low-mass haloes are tightly constrained by the two data sets, and the analysis
reveals several generic failures of models that similarly apply to other
existing SAMs. First, based on the assumption that baryon accretion follows the
dark matter accretion, large mass-loading factors are required for haloes with
circular velocities lower than 200 km/s, and most of the wind mass must be
expelled from the haloes. Second, assuming that the feedback is powered by
Type-II supernovae with a Chabrier IMF, the outflow requires more than 25% of
the available SN kinetic energy. Finally, the posterior predictive
distributions for the star formation history are dramatically inconsistent with
observations for masses similar to or smaller than the Milky-Way mass. The
inferences suggest that the current model family is still missing some key
physical processes that regulate the gas accretion and star formation in
galaxies with masses below that of the Milky Way.Comment: 17 pages, 9 figures, 1 table, accepted for publication in MNRA
Constraining the Star Formation Histories in Dark Matter Halos: I. Central Galaxies
Using the self-consistent modeling of the conditional stellar mass functions
across cosmic time by Yang et al. (2012), we make model predictions for the
star formation histories (SFHs) of {\it central} galaxies in halos of different
masses. The model requires the following two key ingredients: (i) mass assembly
histories of central and satellite galaxies, and (ii) local observational
constraints of the star formation rates of central galaxies as function of halo
mass. We obtain a universal fitting formula that describes the (median) SFH of
central galaxies as function of halo mass, galaxy stellar mass and redshift. We
use this model to make predictions for various aspects of the star formation
rates of central galaxies across cosmic time. Our main findings are the
following. (1) The specific star formation rate (SSFR) at high increases
rapidly with increasing redshift [] for halos of a given
mass and only slowly with halo mass () at a given , in
almost perfect agreement with the specific mass accretion rate of dark matter
halos. (2) The ratio between the star formation rate (SFR) in the main-branch
progenitor and the final stellar mass of a galaxy peaks roughly at a constant
value, , independent of halo mass or the
final stellar mass of the galaxy. However, the redshift at which the SFR peaks
increases rapidly with halo mass. (3) More than half of the stars in the
present-day Universe were formed in halos with 10^{11.1}\msunh < M_h <
10^{12.3}\msunh in the redshift range . (4) ... [abridged]Comment: 15 figures, 22 pages, Accepted for publication in Ap
Star Formation and Stellar Mass Assembly in Dark Matter Halos: From Giants to Dwarfs
The empirical model of Lu et al. 2014 is updated with recent data and used to
study galaxy star formation and assembly histories. At , the predicted
galaxy stellar mass functions are steep, and a significant amount of star
formation is hosted by low-mass haloes that may be missed in current
observations. Most of the stars in cluster centrals formed earlier than
but have been assembled much later. Milky Way mass galaxies have
had on-going star formation without significant mergers since , and
are thus free of significant (classic) bulges produced by major mergers. In
massive clusters, stars bound in galaxies and scattered in the halo form a
homogeneous population that is old and with solar metallicity. In contrast, in
Milky Way mass systems the two components form two distinct populations, with
halo stars being older and poorer in metals by a factor of . Dwarf
galaxies in haloes with have experienced a
star formation burst accompanied by major mergers at , followed by a
nearly constant star formation rate after . The early burst leaves a
significant old stellar population that is distributed in spheroids.Comment: 17 pages, 17 figure
Galactic Coronae in the Intracluster Environment: Semi-confined Stellar-feedback-driven Outflows
Recently X-ray observations have shown the common presence of compact
galactic coronae around intermediate-mass spheroid galaxies embedded in the
intracluster/intragroup medium (ICM). We conduct 2-D hydrodynamic simulations
to study the quasi-steady-state properties of such coronae as the natural
products of the ongoing distributed stellar feedback semi-confined by the
thermal and ram pressures of the ICM. We find that the temperature of a
simulated corona depends primarily on the specific energy of the feedback,
consistent with the lack of the correlation between the observed hot gas
temperature and K-band luminosity of galaxies. The simulated coronae typically
represent subsonic outflows, chiefly because of the semi-confinement. As a
result, the hot gas density increases with the ICM thermal pressure. The ram
pressure, on the other hand, chiefly affects the size and lopsidedness of the
coronae. The density increase could lead to the compression of cool gas clouds,
if present, and hence the formation of stars. The increase also enhances
radiative cooling of the hot gas, which may fuel central supermassive black
holes, explaining the higher frequency of active galactic nuclei observed in
clusters than in the field. The radiation enhancement is consistent with a
substantially higher surface brightness of the X-ray emission detected from
coronae in cluster environment. The total X-ray luminosity of a corona,
however, depends on the relative importance of the surrounding thermal and ram
pressures. These environment dependences should at least partly explain the
large dispersion in the observed diffuse X-ray luminosities of spheroids with
similar stellar properties. Furthermore, we show that an outflow powered by the
distributed feedback can naturally produce a positive radial gradient in the
hot gas entropy, mimicking a cooling flow.Comment: accepted by MNRAS, comments are welcom
An Empirical Model for the Star Formation History in Dark Matter Halos
We develop an empirical approach to infer the star formation rate in dark matter haloes from the galaxy stellar mass function (SMF) at different redshifts and the local cluster galaxy luminosity function (CGLF), which has a steeper faint end relative to the SMF of local galaxies. As satellites are typically old galaxies which have been accreted earlier, this feature can cast important constraint on the formation of low-mass galaxies at high redshift. The evolution of the SMFs suggests the star formation in high-mass haloes (\u3e1012 h−1 M⊙) has to be boosted at high redshift beyond what is expected from a simple scaling of the dynamical time. The faint end of the CGLF implies a characteristic redshift zc ≈ 2 above which the star formation rate in low-mass haloes with masses \u3c1011 h−1 M⊙ must be enhanced relative to that at lower z. This is not directly expected from the standard stellar feedback models. Also, this enhancement leads to some interesting predictions, for instance, a significant old stellar population in present-day dwarf galaxies with M⋆ ≤ 108 h−2 M⊙ and steep slopes of high-redshift stellar mass and star formation rate functions
8-Br-cGMP activates HSPB6 and increases the antineoplastic activity of quinidine in prostate cancer
Abstract Heat shock protein family B [small] member 6 (HSPB6), widely found in various muscles, has been recently identified as a tumor suppressor gene. However, its role in prostate cancer remains unexplored. Herein, we investigated the expression of HSPB6 in prostate cancer and its association with prognosis. Our findings revealed that HSPB6 downregulation in prostate cancer correlated with a poor prognosis. Moreover, we discovered that HSPB6 can be phosphorylated and activated by 8-Br-cGMP, leading to apoptosis in prostate cancer cells by activating Cofilin. Additionally, we demonstrated that knocking down E2F1 by quinidine administration enhances the transcriptional level of HSPB6. Furthermore, we evaluated the combination of quinidine and 8-Br-cGMP as a potential therapeutic strategy for prostate cancer. Our results revealed that the combined treatment was more effective than either treatment alone in inhibiting the growth of prostate cancer through the HSPB6 pathway, both in vitro and in vivo. Overall, our study provides compelling evidence that HSPB6 suppresses malignant behavior in prostate cancer by inducing apoptosis. The combination of quinidine and 8-Br-cGMP emerges as a promising approach for the treatment of prostate cancer