Cool outflows in galaxies and their implications Veilleux, Sylvain; Maiolino, Roberto; Bolatto, Alberto D. ...
The Astronomy and astrophysics review,
12/2020, Letnik:
28, Številka:
1
Journal Article
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Neutral-atomic and molecular outflows are a common occurrence in galaxies, near and far. They operate over the full extent of their galaxy hosts, from the innermost regions of galactic nuclei to the ...outermost reaches of galaxy halos. They carry a substantial amount of material that would otherwise have been used to form new stars. These cool outflows may have a profound impact on the evolution of their host galaxies and environments. This article provides an overview of the basic physics of cool outflows, a comprehensive assessment of the observational techniques and diagnostic tools used to characterize them, a detailed description of the best-studied cases, and a more general discussion of the statistical properties of these outflows in the local and distant universe. The remaining outstanding issues that have not yet been resolved are summarized at the end of the review to inspire new research directions.
We explore the basic parameters that drive the evolution of the fundamental properties of star-forming galaxies within the ‘gas regulator model’, or bathtub-model. From the five basic equations of ...the typical gas regulator model, we derive the general analytic form of the evolution of the key galaxy properties, i.e. gas mass, star formation rate (SFR), stellar mass, specific SFR (sSFR), gas fraction, gas phase metallicity and stellar metallicity, without assuming that galaxies live in the equilibrium state. We find that the timescale required to reach equilibrium, τeq, which is determined by the product of star formation efficiency ε and mass-loading factor λ, is the central parameter in the gas regulator model that is essentially in control of the evolution of all key galaxy properties. The scatters in most of the key scaling relations, such as the stellar mass–SFR relation and stellar mass–metallicity relation, are primarily governed by τeq. Most strikingly, the predicted sSFR evolution is controlled solely by τeq (apart from the cosmic time), independent of the gas inflow rate and of the individual values of ε and λ. Although the precise evolution of the sSFR depends on τeq, the sSFR history is largely insensitive to different values of τeq. The difference between the minimum and maximum sSFR at any epoch is less than a factor of 4 for any given values of τeq. The shape of the predicted sSFR history simply mimics that of the specific mass increase rate of the dark matter halos (sMIRDM) with the typical value of the sSFR around 2 × sMIRDM. We show that the predicted sSFR from the gas regulator model is in good agreement with the predictions from typical semi-analytic models (SAMs), but both are fundamentally different from the observed sSFR history. This clearly implies that some key process is missing in both typical SAMs and gas regulator model, and we hint at some possible culprit. We emphasize the critical role of τeq in controlling the evolution of the galaxy population, especially for gas rich low-mass galaxies and dwarf galaxies that are very unlikely to live around the equilibrium state at any epoch and this has been largely ignored in many similar studies.
We present new ALMA band-7 data for a sample of six luminous quasars at , powered by fast-growing supermassive black holes (SMBHs) with rather uniform properties: the typical accretion rates and ...black hole masses are and . Our sample consists of three "FIR-bright" sources, which were individually detected in previous Herschel/SPIRE observations, with star formation rates of , and three "FIR-faint" sources for which Herschel stacking analysis implies a typical SFR of ∼400 . The dusty interstellar medium in the hosts of all six quasars is clearly detected in the ALMA data and resolved on scales of ∼2 kpc, in both continuum ( ) and line emission. The continuum emission is in good agreement with the expectations from the Herschel data, confirming the intense SF activity in the quasar hosts. Importantly, we detect companion sub-millimeter galaxies (SMGs) for three sources-one FIR-bright and two FIR-faint, separated by and from the quasar hosts. The -based dynamical mass estimates for the interacting SMGs are within a factor of ∼3 of the quasar hosts' masses, while the continuum emission implies . Our ALMA data therefore clearly support the idea that major mergers are important drivers for rapid early SMBH growth. However, the fact that not all high-SFR quasar hosts are accompanied by interacting SMGs and the gas kinematics as observed by ALMA suggest that other processes may be fueling these systems. Our analysis thus demonstrates the diversity of host galaxy properties and gas accretion mechanisms associated with early and rapid SMBH growth.
We explore the dependence of the galaxy mass-metallicity relation on environment in SDSS, in terms of both over-density and central/satellite dichotomy. We find that at a given stellar mass, there is ...a strong dependence of metallicity on over-density for star-forming satellites (i.e. all galaxies members of groups/clusters which are not centrals). High metallicity satellites reside, on average, in regions four times denser than the low metallicity ones. Instead, for star-forming centrals no correlation is found. Star-forming satellites at different stellar masses form a tight sequence in the average over-density - metallicity plane, which covers the entire observed range of metallicities and stellar masses. This remarkable result appears to imply that there exists a universal evolutionary path for all star-forming satellites, regardless of their stellar masses. The strong correlation between over-density and metallicity for star-forming satellites indicates that the gas inflow of satellite galaxies is progressively metal-enriched in denser regions. We interpret our results by employing the gas regulator model and find that the metallicity of the enriched inflow of star-forming satellite galaxies, Z
0, sat, strongly increases with increasing over-density. The derived Z
0, sat- overdensity relation is largely independent of stellar mass and can be well described by a simple power law. If the metallicity of the inflow of star-forming satellites can represent the metallicity of the IGM, then the implied metallicity of the IGM rises from ∼0.01 Z in the void-like environment to ∼0.3 Z in the cluster-like environment, in broad agreement with observations. We show that the observed metallicity difference between star-forming centrals and star-forming satellites becoming smaller towards high stellar masses can be simply explained by the mass-independent enriched inflow, without the need to involve any mass-dependent environmental effect on metallicity. Since satellite galaxies account for at least half of the galaxy population, our findings prompt for a revision of many galaxy evolutionary models, which generally assume pristine gas inflows.
Abstract
We study the gas phase metallicity (O/H) and nitrogen abundance gradients traced by star-forming regions in a representative sample of 550 nearby galaxies in the stellar mass range ...109–1011.5 M⊙ with resolved spectroscopic data from the Sloan Digital Sky Survey IV Mapping Nearby Galaxies at Apache Point Observatory survey. Using strong-line ratio diagnostics (R23 and O3N2 for metallicity and N2O2 for N/O) and referencing to the effective (half-light) radius (Re), we find that the metallicity gradient steepens with stellar mass, lying roughly flat among galaxies with log (M⋆/M⊙) = 9.0 but exhibiting slopes as steep as −0.14 dex $R_{\rm e}^{-1}$ at log (M⋆/M⊙) = 10.5 (using R23, but equivalent results are obtained using O3N2). At higher masses, these slopes remain typical in the outer regions of our sample (R > 1.5Re), but a flattening is observed in the central regions (R < 1Re). In the outer regions (R > 2.0Re), we detect a mild flattening of the metallicity gradient in stacked profiles, although with low significance. The N/O ratio gradient provides complementary constraints on the average chemical enrichment history. Unlike the oxygen abundance, the average N/O profiles do not flatten out in the central regions of massive galaxies. The metallicity and N/O profiles both depart significantly from an exponential form, suggesting a disconnect between chemical enrichment and stellar mass surface density on local scales. In the context of inside-out growth of discs, our findings suggest that central regions of massive galaxies today have evolved to an equilibrium metallicity, while the nitrogen abundance continues to increase as a consequence of delayed secondary nucleosynthetic production.
Abstract
JWST is revolutionizing our understanding of the high-
z
Universe by expanding the black hole horizon, looking farther and to smaller masses, and revealing the stellar light of their hosts. ...By examining JWST galaxies at
z
= 4–7 that host H
α
-detected black holes, we investigate (i) the high-
z
M
•
–
M
⋆
relation and (ii) the black hole mass distribution, especially in its low-mass range (
M
•
≲ 10
6.5
M
⊙
). With a detailed statistical analysis, our findings conclusively reveal a high-
z
M
•
–
M
⋆
relation that deviates at >3
σ
confidence level from the local relation. The high-
z
relation is
log
(
M
•
/
M
⊙
)
=
−
2.43
−
0.83
+
0.83
+
1.06
−
0.09
+
0.09
log
(
M
⋆
/
M
⊙
)
. Black holes are overmassive by ∼10–100× compared to their low-
z
counterparts in galactic hosts of the same stellar mass. This fact is not due to a selection effect in surveys. Moreover, our analysis predicts the possibility of detecting in high-
z
JWST surveys 5–15× more black holes with
M
•
≲ 10
6.5
M
⊙
, and 10–30× more with
M
•
≲ 10
8.5
M
⊙
, compared to local relation’s predictions. The lighter black holes preferentially occupy galaxies with a stellar mass of ∼10
7.5
–10
8
M
⊙
. We have yet to detect these sources because (i) they may be inactive (duty cycles 1%–10%), (ii) the host overshines the active galactic nucleus (AGN), or (iii) the AGN is obscured and not immediately recognizable by line diagnostics. A search of low-mass black holes in existing JWST surveys will further test the
M
•
–
M
⋆
relation. Current JWST fields represent a treasure trove of black hole systems at
z
= 4–7; their detection will provide crucial insights into their early evolution and coevolution with their galactic hosts.
ABSTRACT
In this paper, we investigate how massive central galaxies cease their star formation by comparing theoretical predictions from cosmological simulations: EAGLE, Illustris, and IllustrisTNG ...with observations of the local Universe from the Sloan Digital Sky Survey (SDSS). Our machine learning (ML) classification reveals supermassive black hole mass (MBH) as the most predictive parameter in determining whether a galaxy is star forming or quenched at redshift z = 0 in all three simulations. This predicted consequence of active galactic nucleus (AGN) quenching is reflected in the observations, where it is true for a range of indirect estimates of MBH via proxies as well as its dynamical measurements. Our partial correlation analysis shows that other galactic parameters lose their strong association with quiescence, once their correlations with MBH are accounted for. In simulations, we demonstrate that it is the integrated power output of the AGN, rather than its instantaneous activity, which causes galaxies to quench. Finally, we analyse the change in molecular gas content of galaxies from star-forming to passive populations. We find that both gas fractions (fgas) and star formation efficiencies (SFEs) decrease upon transition to quiescence in the observations but SFE is more predictive than fgas in the ML passive/star-forming classification. These trends in the SDSS are most closely recovered in IllustrisTNG and are in direct contrast with the predictions made by Illustris. We conclude that a viable AGN feedback prescription can be achieved by a combination of preventative feedback and turbulence injection which together quench star formation in central galaxies.
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