Using archival data from the Chandra X-ray telescope, we have measured the spatial extent of the hot interstellar gas in a sample of 49 nearby interacting galaxy pairs, mergers, and merger remnants. For systems with SFR > 1 M(sun)/yr, the volume and mass of hot gas are strongly and linearly correlated with the star formation rate (SFR). This supports the idea that stellar/supernovae feedback dominates the production of hot gas in these galaxies. We compared the mass of X-ray-emitting hot gas Mx(gas) with the molecular and atomic hydrogen interstellar gas masses in these galaxies (M(H2) and M(HI), respectively), using published carbon monoxide and 21 cm HI measurements. Systems with higher SFRs have larger Mx(gas)/(M(H2) + M(HI)) ratios on average, in agreement with recent numerical simulations of star formation and feedback in merging galaxies. The Mx(gas)/(M(H2) + M(HI)) ratio also increases with dust temperature on average. The ratio Mx(gas)/SFR is anti-correlated with the IRAS 60 micron to 100 micron flux ratio and with the Spitzer 3.6 micron to 24 micron. These trends may be due to variations in the spatial density of young stars, the stellar age, the ratio of young to old stars, the initial mass function, and/or the efficiency of stellar feedback. Galaxies with low SFR (<1 M(sun)/yr) and high K band luminosities may have an excess of hot gas relative to the relation for higher SFR galaxies, while galaxies with low K band luminosities (and therefore low stellar masses) may have a deficiency in hot gas, but our sample is not large enough for strong statistical significance.
Star formation rates in the centers of disk galaxies often vastly exceed those at larger radii. We investigate the idea that these central starbursts are self-regulated, with the momentum flux injected to the ISM by star formation balancing the gravitational force confining the gas. For most starbursts, supernovae are the largest contributor to the momentum flux, and turbulence provides the main pressure support for the predominantly-molecular ISM. If the momentum feedback per stellar mass formed is p_*/m_* ~ 3000 km/s, the predicted star formation rate is Sigma_SFR=2 pi G Sigma^2 m_*/p_* ~0.1…
We explore the self-regulation of star formation using a large suite of high resolution hydrodynamic simulations, focusing on molecule-dominated regions (galactic centers and [U]LIRGS) where feedback from star formation drives highly supersonic turbulence. In equilibrium the total midplane pressure, dominated by turbulence, must balance the vertical weight of the ISM. Under self-regulation, the momentum flux injected by feedback evolves until it matches the vertical weight. We test this flux balance in simulations spanning a range of parameters, including surface density $Σ$, momentum injected…
We present the evolution of dust and molecular gas properties in a sample of 11 $z\sim0.03$ starburst to post-starburst (PSB) galaxies selected to span an age sequence from ongoing starburst to 1 Gyr after the starburst ended. All PSBs harbour significant molecular gas and dust reservoirs and residual star formation, indicating that complete quenching of the starburst due to exhaustion or expulsion of gas has not occurred during this timespan. As the starburst ages, we observe a clear decrease in the star-formation efficiency, molecular gas and SFR surface density, and effective dust temperatu…
Galactic winds are essential to regulation of star formation in galaxies. To study the distribution and dynamics of molecular gas in a wind, we imaged the nearby starburst galaxy NGC 1482 in CO ($J=1\rightarrow0$) at a resolution of 1'' ($\approx100$ pc) using the Atacama Large Millimeter/submillimeter Array. Molecular gas is detected in a nearly edge-on disk with a radius of 3 kpc and a biconical outflow emerging from the central 1 kpc starburst and extending to at least 1.5 kpc perpendicular to the disk. In the outflow, CO gas is distributed approximately as a cylindrically symmetrical envel…
The strong time-dependence of the dynamics of galactic bars yields a complex and rapidly evolving distribution of dense gas and star forming regions. Although bars mainly host regions void of any star formation activity, their extremities can gather the physical conditions for the formation of molecular complexes and mini-starbursts. Using a sub-parsec resolution hydrodynamical simulation of a Milky Way-like galaxy, we probe these conditions to explore how and where bar (hydro-)dynamics favours the formation or destruction of molecular clouds and stars. The interplay between the kpc-scale dyna…
We present a detailed assessment of the global atomic hydrogen gas fraction in a sample of post-merger galaxies identified in the Sloan Digital Sky Survey (SDSS). Archival HI measurements of 47 targets are combined with new Arecibo observations of a further 51 galaxies. The stellar mass range of the post-merger sample, our observing strategy, detection thresholds and data analysis procedures replicate those of the extended GALEX Arecibo SDSS Survey (xGASS) which can therefore be used as a control sample. Our principal results are: 1) The post-merger sample shows a ~50 per cent higher HI detect…
We present high-resolution (1".0) Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO (1-0) and CO (2- 1) rotational transitions toward the nearby IR-luminous merger NGC 1614 supplemented with ALMA archival data of CO (3-2), and CO (6-5) transitions. The CO (6-5) emission arises from the starburst ring (central 590 pc in radius), while the lower-$J$ CO lines are distributed over the outer disk ($\sim$ 3.3 kpc in radius). Radiative transfer and photon dominated region (PDR) modeling reveal that the starburst ring has a single warmer gas component with more intense far-ultravi…
Observations of AGN have suggested a possible delay between the peak of star formation (on some scale) and AGN activity. Inefficient fueling (and/or feedback) from fast stellar winds has been invoked to explain this, but we argue this is unlikely in bright systems accreting primarily cold dense gas. We show that such a delay can arise even in bright quasars for purely dynamical reasons. If some large-scale process produces rapid inflow, smaller scales will quickly become gas-dominated. As the gas density peaks, so does the SFR. However, gravitational torques which govern further inflow are rel…
We performed a series of 29 gasdynamical simulations of disc galaxies, barred and unbarred, with various stellar masses, to study the impact of the bar on star formation history. Unbarred galaxies evolve very smoothly, with a star formation rate (SFR) that varies by at most a factor of three over a period of 2 Gyr. The evolution of barred galaxies is much more irregular, especially at high stellar masses. In these galaxies, the bar drives a substantial amount of gas toward the centre, resulting in a high SFR, and producing a starburst in the most massive galaxies. Most of the gas is converted …
We characterise the physical nature of a 1.1 mm-selected, flux-limited, and interferometrically followed up sample of SMGs in COSMOS. We used the MAGPHYS code to fit the multiwavelength (UV-radio) SEDs of 16 of the target SMGs. We also constructed the pure radio SEDs of our SMGs using three different radio bands (325 MHz, 1.4 GHz, and 3 GHz). Moreover, since two SMGs in our sample, AzTEC1 and AzTEC3, benefit from previous CO line observations, we studied their properties in more detail. We found that 63% of our target SMGs lie above the galaxy main-sequence by more than a factor of 3, and henc…
SQuIGG$\vec{L}$E: Spatially resolved NIRSpec Pa$α$ reveals that the most CO-luminous, $z\sim0.7$ post-starburst galaxies exhibit falling---but still active---star formation behind optically thick dust
The Johns Hopkins University（约翰斯·霍普金斯大学）；Princeton University（普林斯顿大学）；University of Pittsburgh（匹兹堡大学）；University of Colorado, Boulder（科罗拉多大学博尔德分校）；Texas A&M University（德克萨斯农工大学）
At redshift z = 2, when the Universe was just three billion years old, half of the most massive galaxies were extremely compact and had already exhausted their fuel for star formation(1-4). It is believed that they were formed in intense nuclear starbursts and that they ultimately grew into the most massive local elliptical galaxies seen today, through mergers with minor companions(5,6), but validating this picture requires higher-resolution observations of their centres than is currently possible. Magnification from gravitational lensing offers an opportunity to resolve the inner regions of g…
Gas excitation of post-starburst galaxies at 0.6 < z < 1.3
Istituto Nazionale di Astrofisica (INAF)（意大利国家天体物理研究所）；Dipartimento di Fisica e Astronomia, Università di Bologna（博洛尼亚大学物理与天文系）；Cosmic Dawn Center (DAWN)（宇宙黎明中心）；DTU Space, Technical University of Denmark（丹麦技术大学空间研究中心）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理学研究所）；INAF – IASF Milano（意大利国家天体物理研究所米兰天文台）
Based on a sample of 79 local advanced merger (adv-merger) (U)LIRGs, we search for the evidence of quenching process by investigating the distributions of the star formation history indicators (EW(H$α$), EW(H$δ$$_A$) and D$_n(4000)$) on the NUV-r color-mass and SFR-$M_{\ast}$ diagrams. The distributions of the EW(H$α$) and D$_n(4000)$ on the NUV-r color-mass diagram show clear trends that at a given stellar mass, galaxies with redder NUV-r colors have smaller EW(H$α$) and larger D$_n(4000)$. The reddest adv-merger (U)LIRGs close to the green valley have D$_n(4000)$$>1.4$ mostly. In addition, i…
To investigate the role of bars in the chemical evolution of isolated disc galaxies, we performed a series of 39 gas dynamical simulations of isolated barred and unbarred galaxies with various masses, initial gas fractions, and AGN feedback models. The presence of a bar drives a substantial amount of gas toward the central region of the galaxy. In the most massive galaxies, this results in a violent starburst, followed by a drop in star formation resulting from gas exhaustion. The time delay between Type Ia and Type II supernovae explosions means that barred galaxies experience a rapid increas…
We explore the relationship between active galactic nuclei and star formation in a sample of 513 optically luminous type 1 quasars up to redshifts of $\sim$4 hosting extremely high star formation rates (SFRs). The quasars are selected to be individually detected by the \textit{Herschel} SPIRE instrument at $> $3$σ$ at 250 $μ$m, leading to typical SFRs of order of 1000 M$_{\odot}$yr$^{-1}$. We find the average SFRs to increase by almost a factor 10 from $z\sim0.5$ to $z\sim3$, mirroring the rise in the comoving SFR density over the same epoch. However, we find that the SFRs remain approximately…
The evolution of galaxies is governed by equations with chaotic solutions: gravity and compressible hydrodynamics. While this micro-scale chaos and stochasticity has been well studied, it is poorly understood how it couples to macro-scale properties examined in simulations of galaxy formation. In this paper, we show how perturbations introduced by floating-point roundoff, random number generators, and seemingly trivial differences in algorithmic behaviour can produce non-trivial differences in star formation histories, circumgalactic medium (CGM) properties, and the distribution of stellar mas…
Recent work suggests blue ellipticals form in mergers and migrate quickly from the blue cloud of star-forming galaxies to the red sequence of passively evolving galaxies, perhaps as a result of black hole feedback. Such rapid reddening of stellar populations implies that large gas reservoirs in the pre-merger star-forming pair must be depleted on short time scales. Here we present pilot observations of atomic hydrogen gas in four blue early-type galaxies that reveal increasing spatial offsets between the gas reservoirs and the stellar components of the galaxies, with advancing post-starburst a…
We introduce the "Engineering Dwarfs at Galaxy formation's Edge" (EDGE) project to study the cosmological formation and evolution of the smallest galaxies in the Universe. In this first paper, we explore the effects of resolution and sub-grid physics on a single low mass halo ($M_{\rm halo}=10^{9}~M_\odot$), simulated to redshift $z=0$ at a mass and spatial resolution of $\sim 20~M_\odot$ and $\sim 3$ pc. We consider different star formation prescriptions, supernova feedback strengths and on-the-fly radiative transfer (RT). We show that RT changes the mode of galactic self-regulation at this h…
The regulation of galactic-scale star formation rates (SFRs) is a basic problem for theories of galaxy formation and evolution: which processes are responsible for making observed star formation rates so inefficient compared to maximal rates of gas content divided by dynamical timescale? Here we study the effect of magnetic fields of different strengths on the evolution of giant molecular clouds (GMCs) within a kiloparsec patch of a disk galaxy and resolving scales down to $\simeq0.5\:{\rm{pc}}$. Including an empirically motivated prescription for star formation from dense gas ($n_{\rm{H}}>10^…
Blue compact dwarf galaxies (BCDs) form stars at, for their sizes, extraordinarily high rates. In this paper, we study what triggers this starburst and what is the fate of the galaxy once its gas fuel is exhausted. We select four BCDs with smooth outer regions, indicating them as possible progenitors of dwarf elliptical galaxies. We have obtained photometric and spectroscopic data with the FORS and ISAAC instruments on the VLT. We analyse their infra-red spectra using a full spectrum fitting technique which yields the kinematics of their stars and ionized gas together with their stellar popula…
We report new ALMA observations of the CO(3-2) line emission from the $2.1\pm0.3\times10^{10}\rm\thinspace M_{\odot}$ molecular gas reservoir in the central galaxy of the Phoenix cluster. The cold molecular gas is fuelling a vigorous starburst at a rate of $500-800\rm\thinspace M_{\odot}\rm\; yr^{-1}$ and powerful black hole activity in the form of both intense quasar radiation and radio jets. The radio jets have inflated huge bubbles filled with relativistic plasma into the hot, X-ray atmospheres surrounding the host galaxy. The ALMA observations show that extended filaments of molecular gas,…
We resolve the host galaxies of seven gravitationally lensed quasars at redshift 1.5 to 2.8 using observations with the Atacama Large (sub-)Millimetre Array. Using a visibility-plane lens modelling technique, we create pixellated reconstructions of the dust morphology, and CO line morphology and kinematics. We find that the quasar hosts in our sample can be distinguished into two types: 1) galaxies characterised by clumpy, extended dust distributions ($R_{\rm eff}\sim2$ kpc) and mean star formation rate surface densities comparable to sub-mm-selected dusty star-forming galaxies ($Σ_{\rm SFR}\s…
The Milky Way in context: The formation of galactic discs and chemical sequences from a cosmological perspective
Universitat de Barcelona（巴塞罗那大学）；Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS（巴黎天文台，PSL大学，索邦大学，巴黎西岱大学，CY塞尔吉巴黎大学，法国国家科学研究中心）；Kavli IPMU (WPI), UTIAS, The University of Tokyo（东京大学 Kavli宇宙粒子与宇宙学研究所（WPI），UTIAS）；Max Planck Institut für Astrophysik（马克斯·普朗克天体物理研究所）；Astrophysics Research Institute, Liverpool John Moores University（利物浦约翰摩尔斯大学天体物理研究所）
We investigate the physics driving the cosmic star formation (SF) history using the more than fifty large, cosmological, hydrodynamical simulations that together comprise the OverWhelmingly Large Simulations (OWLS) project. We systematically vary the parameters of the model to determine which physical processes are dominant and which aspects of the model are robust. Generically, we find that SF is limited by the build-up of dark matter haloes at high redshift, reaches a broad maximum at intermediate redshift, then decreases as it is quenched by lower cooling rates in hotter and lower density g…
