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Register a new userGas-phase Metallicity as a Diagnostic of the Drivers of Star-formation on Different Spatial Scales
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We examine the correlations of star formation rate (SFR) and gas-phase metallicity $Z$. We first predict how the SFR, cold gas mass and $Z$ will change with variations in inflow rate or in star-formation efficiency (SFE) in a simple gas-regulator framework. The changes $Delta {rm log}$SFR and $Delta {rm log} Z$, are found to be negatively (positively) correlated when driving the gas-regulator with time-varying inflow rate (SFE). We then study the correlation of $Delta {rm log}$sSFR (specific SFR) and $Delta {rm log}$(O/H) from observations, at both $sim$100 pc and galactic scales, based on two 2-dimensional spectroscopic surveys with different spatial resolutions, MAD and MaNGA. After taking out the overall mass and radial dependences, which may reflect changes in inflow gas metallicity and/or outflow mass-loading, we find that $Delta {rm log}$sSFR and $Delta {rm log}$(O/H) on galactic are found to be negatively correlated, but $Delta {rm log}$sSFR and $Delta {rm log}$(O/H) are positively correlated on $sim$100 pc scales within galaxies. If we assume that the variations across the population reflect temporal variations in individual objects, we conclude that variations in the star formation rate are primarily driven by time-varying inflow at galactic scales, and driven by time-varying SFE at $sim$100 pc scales. We build a theoretical framework to understand the correlation between SFR, gas mass and metallicity, as well as their variability, which potentially uncovers the relevant physical processes of star formation at different scales.
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We present a full high resolution SPIRE FTS spectrum of the nearby ultraluminous infrared galaxy Mrk231. In total 25 lines are detected, including CO J=5-4 through J=13-12, 7 rotational lines of H2O, 3 of OH+ and one line each of H2O+, CH+, and HF. We find that the excitation of the CO rotational levels up to J=8 can be accounted for by UV radiation from star formation. However, the approximately flat luminosity distribution of the CO lines over the rotational ladder above J=8 requires the presence of a separate source of excitation for the highest CO lines. We explore X-ray heating by the accreting supermassive black hole in Mrk231 as a source of excitation for these lines, and find that it can reproduce the observed luminosities. We also consider a model with dense gas in a strong UV radiation field to produce the highest CO lines, but find that this model strongly overpredicts the hot dust mass in Mrk231. Our favoured model consists of a star forming disk of radius 560 pc, containing clumps of dense gas exposed to strong UV radiation, dominating the emission of CO lines up to J=8. X-rays from the accreting supermassive black hole in Mrk231 dominate the excitation and chemistry of the inner disk out to a radius of 160 pc, consistent with the X-ray power of the AGN in Mrk231. The extraordinary luminosity of the OH+ and H2O+ lines reveals the signature of X-ray driven excitation and chemistry in this region.
The results of a detailed analysis of SMA, VLA, and IRAM observations of the region of massive star formation S255N in CO(2---1), h, hh, co and some other lines is presented. Combining interferometer and single-dish data has enabled a more detailed investigation of the gas kinematics in the moleclar core on various spatial scales. There are no signs of rotation or isotropic compression on the scale of the region as whole. The largest fragments of gas ($approx$0.3 pc) are located near the boundary of the regions of ionized hydrogen S255 and S257. Some smaller-scale fragments are associated with protostellar clumps. The kinetic temperatures of these fragments lie in the range 10---80 K. A circumstellar torus with inner radius R$_{in}$ $approx$ 8000 AU and outer radius R$_{out}$ 12 000 AU has been detected around the clump SMA1. The rotation profile indicates the existence of a central object with mass $approx$ 8.5/ sin 2 (i) M$_odot$ . SMA1 is resolved into two clumps, SMA1---NE and SMA1---SE, whose temperatures are $approx$150 K and $approx$25 K, respectively. To all appearances, the torus is involved in the accretion of surrounding gas onto the two protostellar clumps.
Using a sample of dwarf galaxies observed using the VIMOS IFU on the VLT, we investigate the mass-metallicity relation (MZR) as a function of star formation rate (FMR$_{text{SFR}}$) as well as HI-gas mass (FMR$_{text{HI}}$). We combine our IFU data with a subsample of galaxies from the ALFALFA HI survey crossmatched to the Sloan Digital Sky Survey to study the FMR$_{text{SFR}}$ and FMR$_{text{HI}}$ across the stellar mass range 10$^{6.6}$ to 10$^{8.8}$ M$_odot$, with metallicities as low as 12+log(O/H) = 7.67. We find the 1$sigma$ mean scatter in the MZR to be 0.05 dex. The 1$sigma$ mean scatter in the FMR$_{text{SFR}}$ (0.02 dex) is significantly lower than that of the MZR. The FMR$_{text{SFR}}$ is not consistent between the IFU observed galaxies and the ALFALFA/SDSS galaxies for SFRs lower than 10$^{-2.4}$ M$_odot$ yr$^{-1}$, however this could be the result of limitations of our measurements in that regime. The lowest mean scatter (0.01 dex) is found in the FMR$_{text{HI}}$. We also find that the FMR$_{text{HI}}$ is consistent between the IFU observed dwarf galaxies and the ALFALFA/SDSS crossmatched sample. We introduce the fundamental metallicity luminosity counterpart to the FMR, again characterized in terms of SFR (FML$_{text{SFR}}$) and HI-gas mass (FML$_{text{HI}}$). We find that the FML$_{text{HI}}$ relation is consistent between the IFU observed dwarf galaxy sample and the larger ALFALFA/SDSS sample. However the 1$sigma$ scatter for the FML$_{text{HI}}$ relation is not improved over the FMR$_{text{HI}}$ scenario. This leads us to conclude that the FMR$_{text{HI}}$ is the best candidate for a physically motivated fundamental metallicity relation.
We explore how the star formation efficiency in a protocluster clump is regulated by metallicity dependent stellar winds from the newly formed massive OB stars (Mstar >5 Msol). The model describes the co-evolution of the mass function of gravitationally bound cores and of the IMF in a protocluster clump. Dense cores are generated uniformly in time at different locations in the clump, and contract over lifetimes that are a few times their free fall times. The cores collapse to form stars that power strong stellar winds whose cumulative kinetic energy evacuates the gas from the clump and quenches further core and star formation. This sets the final star formation efficiency, SFEf. Models are run with various metallicities in the range Z/Zsol=[0.1,2]. We find that the SFEf decreases strongly with increasing metallicity.The SFEf-metallicity relation is well described by a decaying exponential whose exact parameters depend weakly on the value of the core formation efficiency. We find that there is almost no dependence of the SFEf-metallicity relation on the clump mass. This is due to the fact that an increase (decrease) in the clump mass leads to an increase (decrease) in the feedback from OB stars which is opposed by an increase (decrease) in the gravitational potential of the clump. The clump mass-cluster mass relations we find for all of the different metallicity cases imply a negligible difference between the exponent of the mass function of the protocluster clumps and that of the young clusters mass function. By normalizing the SFEs to their value for the solar metallicity case, we compare our results to SFE-metallicity relations derived on galactic scales and find a good agreement. As a by-product of this study, we also provide ready-to-use prescriptions for the power of stellar winds of main sequence OB stars in the mass range [5,80] Msol in the metallicity range we have considered
Present-day clusters are massive halos containing mostly quiescent galaxies, while distant protoclusters are extended structures containing numerous star-forming galaxies. We investigate the implications of this fundamental change in a cosmological context using a set of N-body simulations and semi-analytic models. We find that the fraction of the cosmic volume occupied by all (proto)clusters increases by nearly three orders of magnitude from z=0 to z=7. We show that (proto)cluster galaxies are an important, and even dominant population at high redshift, as their expected contribution to the cosmic star-formation rate density rises (from 1% at z=0) to 20% at z=2 and 50% at z=10. Protoclusters thus provide a significant fraction of the cosmic ionizing photons, and may have been crucial in driving the timing and topology of cosmic reionization. Internally, the average history of cluster formation can be described by three distinct phases: at z~10-5, galaxy growth in protoclusters proceeded in an inside-out manner, with centrally dominant halos that are among the most active regions in the Universe; at z~5-1.5, rapid star formation occurred within the entire 10-20 Mpc structures, forming most of their present-day stellar mass; at z<~1.5, violent gravitational collapse drove these stellar contents into single cluster halos, largely erasing the details of cluster galaxy formation due to relaxation and virialization. Our results motivate observations of distant protoclusters in order to understand the rapid, extended stellar growth during Cosmic Noon, and their connection to reionization during Cosmic Dawn.
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