A comprehensive view of the interstellar medium in a quasar host galaxy at z ≈ 6.4

GalaxiesInterstellar matter and star formatio

SHINING, A Survey of Far-infrared Lines in Nearby Galaxies. I. Survey Description, Observational Trends, and Line Diagnostics

We use the Herschel/PACS spectrometer to study the global and spatially resolved far-infrared (FIR) fine-structure line emission in a sample of 52 galaxies that constitute the SHINING survey. These galaxies include star-forming, active-galactic nuclei (AGN), and luminous infrared galaxies (LIRGs). We find an increasing number of galaxies (and kiloparsec size regions within galaxies) with low line-to-FIR continuum ratios as a function of increasing FIR luminosity ($L_{\mathrm{FIR}}$), dust infrared color, $L_{\mathrm{FIR}}$ to molecular gas mass ratio ($L_{\mathrm{FIR}}/M_{\mathrm{mol}}$), and FIR surface brightness ($\Sigma_{\mathrm{FIR}}$). The correlations between the [CII]/FIR or [OI]/FIR ratios with $\Sigma_{\mathrm{FIR}}$ are remarkably tight ($\sim0.3$ dex scatter over almost four orders of magnitude in $\Sigma_{\mathrm{FIR}}$). We observe that galaxies with $L_{\mathrm{FIR}}/M_{\mathrm{mol}} \gtrsim 80\,L_{\odot}\,M_{\odot}^{-1}$ and $\Sigma_{\mathrm{FIR}}\gtrsim10^{11}$ $L_{\odot}$ kpc$^{-2}$ tend to have weak fine-structure line-to-FIR continuum ratios, and that LIRGs with infrared sizes $\gtrsim1$ kpc have line-to-FIR ratios comparable to those observed in typical star-forming galaxies. We analyze the physical mechanisms driving these trends in Paper II (Herrera-Camus et al. 2018). The combined analysis of the [CII], [NII], and [OIII] lines reveals that the fraction of the [CII] line emission that arises from neutral gas increases from 60% to 90% in the most active star-forming regions and that the emission originating in the ionized gas is associated with low-ionization, diffuse gas rather than with dense gas in HII regions. Finally, we report the global and spatially resolved line fluxes of the SHINING galaxies to enable the comparison and planning of future local and high-$z$ studies

HARDWARE.astronomy

An open-source hardware initiative for astronom

A benchmark for extreme conditions of the multiphase interstellar medium in the most luminous hot dust-obscured galaxy at <i>z</i> = 4.6

WISE J224607.6–052634.9 (W2246–0526) is a hot dust-obscured galaxy at z = 4.601, and the most luminous obscured quasar known to date. W2246–0526 harbors a heavily obscured supermassive black hole that is most likely accreting above the Eddington limit. We present observations with the Atacama Large Millimeter/submillimeter Array (ALMA) in seven bands, including band 10, of the brightest far-infrared (FIR) fine-structure emission lines of this galaxy: [OI]63 μm, [OIII]88 μm, [NII]122 μm, [OI]145 μm, [CII]158 μm, [NII]205 μm, [CI]370 μm, and [CI]609 μm. A comparison of the data to a large grid of CLOUDY radiative transfer models reveals that a high hydrogen density (nH ∼ 3 × 103 cm−3) and extinction (AV ∼ 300 mag), together with extreme ionization (log(U) = − 0.5) and a high X-ray to UV ratio (αox ≥ −0.8) are required to reproduce the observed nuclear line ratios. The values of αox and U are among the largest found in the literature and imply the existence of an X-ray-dominated region (XDR). In fact, this component explains the a priori very surprising non-detection of the [OIII]88 μm emission line, which is actually suppressed, instead of boosted, in XDR environments. Interestingly, the best-fitted model implies higher X-ray emission and lower CO content than what is detected observationally, suggesting the presence of a molecular gas component that should be further obscuring the X-ray emission over larger spatial scales than the central region that is being modeled. These results highlight the need for multiline infrared observations to characterize the multiphase gas in high redshift quasars and, in particular, W2246–0526 serves as an extreme benchmark for comparisons of interstellar medium conditions with other quasar populations at cosmic noon and beyond

The nature of the [C ii] emission in dusty star-forming galaxies from the SPT survey

We present [CII] observations of 20 strongly lensed dusty star forming galaxies at 2.1 < z < 5.7 using APEX and Herschel. The sources were selected on their 1.4 mm flux (S_1.4mm > 20 mJy) from the South Pole Telescope survey, with far-infrared (FIR) luminosities determined from extensive photometric data. The [CII] line is robustly detected in 17 sources, all but one being spectrally resolved. Eleven out of 20 sources observed in [CII] also have low-J CO detections from ATCA. A comparison with mid- and high-J CO lines from ALMA reveals consistent [CII] and CO velocity profiles, suggesting that there is little differential lensing between these species. The [CII], low-J CO and FIR data allow us to constrain the properties of the interstellar medium. We find [CII] to CO(1-0) luminosity ratios in the SPT sample of 5200 +- 1800, with significantly less scatter than in other samples. This line ratio can be best described by a medium of [CII] and CO emitting gas with a higher [CII] than CO excitation temperature, high CO optical depth tau_CO >> 1, and low to moderate [CII] optical depth tau_CII ~< 1. The geometric structure of photodissociation regions allows for such conditions.Comment: 19 Pages, 12 figures, accepted for publication in MNRA

Galaxy growth in a massive halo in the first billion years of cosmic history

According to the current understanding of cosmic structure formation, the precursors of the most massive structures in the Universe began to form shortly after the Big Bang, in regions corresponding to the largest fluctuations in the cosmic density field(1-3). Observing these structures during their period of active growth and assembly-the first few hundred million years of the Universe-is challenging because it requires surveys that are sensitive enough to detect the distant galaxies that act as signposts for these structures and wide enough to capture the rarest objects. As a result, very few such objects have been detected so far(4,5). Here we report observations of a far-infrared-luminous object at redshift 6.900 (less than 800 million years after the Big Bang) that was discovered in a wide-field survey(6). High-resolution imaging shows it to be a pair of extremely massive star-forming galaxies. The larger is forming stars at a rate of 2,900 solar masses per year, contains 270 billion solar masses of gas and 2.5 billion solar masses of dust, and is more massive than any other known object at a redshift of more than 6. Its rapid star formation is probably triggered by its companion galaxy at a projected separation of 8 kiloparsecs. This merging companion hosts 35 billion solar masses of stars and has a star-formation rate of 540 solar masses per year, but has an order of magnitude less gas and dust than its neighbour and physical conditions akin to those observed in lower-metallicity galaxies in the nearby Universe(7). These objects suggest the presence of a dark-matter halo with a mass of more than 100 billion solar masses, making it among the rarest dark-matter haloes that should exist in the Universe at this epoch