Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userHow galaxies form stars: the connection between local and global star formation in galaxy simulations
100
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Using a suite of isolated $L_star$ galaxy simulations, we show that global depletion times and star-forming gas mass fractions in simulated galaxies exhibit systematic and well-defined trends as a function of the local star formation efficiency per freefall time, $epsilon_{rm ff}$, strength of stellar feedback, and star formation threshold. We demonstrate that these trends can be reproduced and explained by a simple physical model of global star formation in galaxies. Our model is based on mass conservation and the idea of gas cycling between star-forming and non-star-forming states on certain characteristic time scales under the influence of dynamical and feedback processes. Both the simulation results and our model predictions exhibit two limiting regimes with rather different dependencies of global galactic properties on the local parameters. When $epsilon_{rm ff}$ is small and feedback is inefficient, the total star-forming mass fraction, $f_{rm sf}$, is independent of $epsilon_{rm ff}$ and the global depletion time, $tau_{rm dep}$, scales inversely with $epsilon_{rm ff}$. When $epsilon_{rm ff}$ is large or feedback is very efficient, these trends are reversed: $f_{rm sf} propto epsilon_{rm ff}^{-1}$ and $tau_{rm dep}$ is independent of $epsilon_{rm ff}$ but scales linearly with the feedback strength. We also compare our results with the observed depletion times and mass fractions of star-forming and molecular gas and show that they provide complementary constraints on $epsilon_{rm ff}$ and the feedback strength. We show that useful constraints on $epsilon_{rm ff}$ can also be obtained using measurements of the depletion time and its scatter on different spatial scales.
rate research
Read More
We study the implementation of mechanical feedback from supernovae (SNe) and stellar mass loss in galaxy simulations, within the Feedback In Realistic Environments (FIRE) project. We present the FIRE-2 algorithm for coupling mechanical feedback, which can be applied to any hydrodynamics method (e.g. fixed-grid, moving-mesh, and mesh-less methods), and black hole as well as stellar feedback. This algorithm ensures manifest conservation of mass, energy, and momentum, and avoids imprinting preferred directions on the ejecta. We show that it is critical to incorporate both momentum and thermal energy of mechanical ejecta in a self-consistent manner, accounting for SNe cooling radii when they are not resolved. Using idealized simulations of single SN explosions, we show that the FIRE-2 algorithm, independent of resolution, reproduces converged solutions in both energy and momentum. In contrast, common fully-thermal (energy-dump) or fully-kinetic (particle-kicking) schemes in the literature depend strongly on resolution: when applied at mass resolution >100 solar masses, they diverge by orders-of-magnitude from the converged solution. In galaxy-formation simulations, this divergence leads to orders-of-magnitude differences in galaxy properties, unless those models are adjusted in a resolution-dependent way. We show that all models that individually time-resolve SNe converge to the FIRE-2 solution at sufficiently high resolution. However, in both idealized single-SN simulations and cosmological galaxy-formation simulations, the FIRE-2 algorithm converges much faster than other sub-grid models without re-tuning parameters.
We present a study of the active galactic nucleus (AGN) activity in the local Universe (z < 0.33) and its correlation with the host galaxy properties, derived from a Sloan Digital Sky Survey (SDSS DR8) sample with spectroscopic star-formation rate (SFR) and stellar mass ($mathcal{M}_{ast}$) determination. To quantify the level of AGN activity we used X-ray information from the XMM-Newton Serendipitous Source Catalogue (3XMM DR8). Applying multiwavelength AGN selection criteria (optical BPT-diagrams, X-ray/optical ratio etc) we found that 24% of the detected sources are efficiently-accreting AGN with moderate-to-high X-ray luminosity, which are twice as likely to be hosted by star-forming galaxies than by quiescent ones. The distribution of the specific Black Hole accretion rate (sBHAR, $lambda_{mathrm{sBHAR}}$) shows that nuclear activity in local, non-AGN dominated galaxies peaks at very low accretion rates ($-4 lesssim loglambda_{mathrm{sBHAR}} lesssim -3$) in all stellar mass ranges. However, we observe systematically larger values of sBHAR for galaxies with active star-formation than for quiescent ones, as well as an increase of the mean $lambda_{mathrm{sBHAR}}$ with SFR for both star-forming and quiescent galaxies. These findings confirm the decreased level of AGN activity with cosmic time and are consistent with a scenario where both star-formation and AGN activity are fuelled by a common gas reservoir.
We explore the connection between dust and star formation, in the context of environmental effects on galaxy evolution. In particular, we exploit the susceptibility of dust to external processes to assess the influence of dense environment on star-forming galaxies. We have selected cluster Abell 1758 from the Local Cluster Substructure Survey (LoCuSS). Its complex dynamical state is an ideal test-bench to track dust removal and destruction in galaxies due to merger and accretion shocks. We present a systematic panchromatic study (from 0.15 $rm mu$m with GALEX to 500 $rm mu$m with Herschel) of spectroscopically confirmed star-forming cluster galaxies at intermediate redshift. We observe that the main subclusters (A1758N and A1758S) belong to two separate large-scale structures, with no overlapping galaxy members. Star-forming cluster members are distributed preferentially outside cluster central regions, and are not grouped in substructures. Rather, these galaxies are being funneled towards the main subclusters along separate accretion filaments. Additionally, we present the first study of dust-to-stellar (DTS) mass ratio used as indicator for local environmental influence on galaxy evolution. Star-forming cluster members show lower mean values (32% at 2.4$rm sigma$) of DTS mass ratio and lower levels of infrared emission from birth clouds with respect to coeval star-forming field galaxies. This picture is consistent with the majority of star-forming cluster members infalling in isolation. Upon accretion, star-formation is observed to decrease and warm dust is destroyed due to heating from the intracluster medium radiation, ram-pressure stripping and merger shocks.
We present a sample of 33 galaxies for which we have calculated (i) the average rate of shear from publish rotation curves, (ii) the far-infrared luminosity from IRAS fluxes and (iii) The K-band luminosity from 2MASS. We show that a correlation exists between the shear rate and the ratio of the far-infrared to K-band luminosity. This ratio is essentially a measure of the star formation rate per unit mass, or the specific star formation rate. From this correlation we show that a critical shear rate exists, above which star formation would turn off in the disks of spiral galaxies. Using the correlation between shear rate and spiral arm pitch angle, this shear rate corresponds to the lowest pitch angles typically measured in near-infrared images of spiral galaxies.
This paper systematically investigates comoving Mpc scale intergalactic medium (IGM) environment around galaxies traced by the Ly$alpha$ forest. Using our cosmological hydrodynamic simulations, we investigate the IGM-galaxy connection at $z=2$ by two methods: (I) cross-correlation analysis between galaxies and the fluctuation of Ly$alpha$ forest transmission ($delta_text{F}$); and (II) comparing the overdensity of neutral hydrogen (HI) and galaxies. Our simulations reproduce observed cross-correlation functions (CCF) between Ly$alpha$ forest and Lyman-break galaxies. We further investigate the variation of the CCF using subsamples divided by dark matter halo mass ($M_text{DH}$), galaxy stellar mass ($M_star$), and star-formation rate (SFR), and find that the CCF signal becomes stronger with increasing $M_text{DH}$, $M_star$, and SFR. The CCFs between galaxies and gas-density fluctuation are also found to have similar trends. Therefore, the variation of the $delta_text{F}$-CCF depending on $M_text{DH}$, $M_star$, and SFR is due to varying gas density around galaxies. We find that the correlation between galaxies and the IGM HI distribution strongly depends on $M_text{DH}$ as expected from the linear theory. Our results support the $Lambda$CDM paradigm, finding a spatial correlation between galaxies and IGM HI, with more massive galaxies being clustered in higher-density regions.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
