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Register a new userFirst Connection between Cold Gas in Emission and Absorption: CO Emission from a Galaxy-Quasar Pair
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M. Neeleman
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We present the first detection of molecular emission from a galaxy selected to be near a projected background quasar using the Atacama Large Millimeter/submillimeter Array (ALMA). The ALMA detection of CO(1$-$0) emission from the $z=0.101$ galaxy toward quasar PKS 0439-433 is coincident with its stellar disk and yields a molecular gas mass of $M_{rm mol} approx 4.2 times 10^9 M_odot$ (for a Galactic CO-to-H$_2$ conversion factor), larger than the upper limit on its atomic gas mass. We resolve the CO velocity field, obtaining a rotational velocity of $134 pm 11$ km s$^{-1}$, and a resultant dynamical mass of $geq 4 times 10^{10} M_odot$. Despite its high metallicity and large molecular mass, the $z=0.101$ galaxy has a low star formation rate, implying a large gas consumption timescale, larger than that typical of late-type galaxies. Most of the molecular gas is hence likely to be in a diffuse extended phase, rather than in dense molecular clouds. By combining the results of emission and absorption studies, we find that the strongest molecular absorption component toward the quasar cannot arise from the molecular disk, but is likely to arise from diffuse gas in the galaxys circumgalactic medium. Our results emphasize the potential of combining molecular and stellar emission line studies with optical absorption line studies to achieve a more complete picture of the gas within and surrounding high-redshift galaxies.
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We investigate the relation between the detection of the $11.3,mu$m PAH feature in the nuclear ($sim 24-230,$pc) regions of 22 nearby Seyfert galaxies and the properties of the cold molecular gas. For the former we use ground-based (0.3-0.6 resolution) mid-infrared (mid-IR) spectroscopy. The cold molecular gas is traced by ALMA and NOEMA high (0.2-1.1) angular resolution observations of the CO(2-1) transition. Galaxies with a nuclear detection of the $11.3,mu$m PAH feature contain more cold molecular gas (median $1.6times 10^7,M_odot$) and have higher column densities ($N({rm H}_2) = 2 times 10^{23},{rm cm}^{-2}$) over the regions sampled by the mid-IR slits than those without a detection. This suggests that molecular gas plays a role in shielding the PAH molecules in the harsh environments of Seyfert nuclei. Choosing the PAH molecule naphthalene as an illustration, we compute its half-life in the nuclear regions of our sample when exposed to 2.5keV hard X-ray photons. We estimate shorter half-lives for naphthalene in nuclei without a $11.3,mu$m PAH detection than in those with a detection. The Spitzer/IRS PAH ratios on circumnuclear scales ($sim$ 4 $sim$ 0.25-1.3kpc) are in between model predictions for neutral and partly ionized PAHs. However, Seyfert galaxies in our sample with the highest nuclear H$_2$ column densities are not generally closer to the neutral PAH tracks. This is because in the majority of our sample galaxies, the CO(2-1) emission in the inner $sim$ 4 is not centrally peaked and in some galaxies traces circumnuclear sites of strong star formation activity. Spatially resolved observations with the MIRI medium-resolution spectrograph (MRS) on the James Webb Space Telescope will be able to distinguish the effects of an active galactic nucleus (AGN) and star formation on the PAH emission in nearby AGN.
What is the expected infrared output of elliptical galaxies? Here we report the latest findings obtained in this high time resolution (~10 years) and high spatial resolution (2.5 parsec at center) study. We add a set of grain physics to the MACER code, including (a) dust grains made in passive stellar evolution; (b) dust grain growth due to collision and sticking; (c) grain destruction due to thermal sputtering; (d) dust cooling of hot gas via inelastic collisions; and (e) radiation pressure on dust grains. The code improvements enable us to analyze the effects of dust on metal depletion and AGN obscuration, and also to assess the infrared output of the modeled galaxies. We simulate a representative massive elliptical galaxy of a central stellar velocity dispersion ~ 260 km/s and modest rotation. We find that: (1) the circumnuclear disk (of a size <~ 1 kpc) is dusty in its outer region where most of the metals are in dust grains, while in the inner disk most of the dust grains are destroyed by the AGN irradiation; (2) the dusty disk is optically thick to both the starlight within the disk and the radiation from the central AGN. Thus the AGN will be obscured behind the disk, and the latter is of a covering factor ~ 0.2; (3) the dust infrared emission is mainly due to the AGN irradiation. The median infrared luminosity is ~ 2e44 erg/s, and it can reach >~ 1e46 erg/s during outbursts; (4) the duty cycles of the AGN activities, star formation, and the dust infrared luminosity roughly match observations, e.g., in most of its lifetime, the simulated galaxy is a stereotypical quiescent elliptical galaxy with L_{IR} ~ 1e11*L_{solar}, while the star formation rate can exceed 250 M_{solar}/yr during central outbursts.
We present a study of cold gas absorption from a damped Lyman-$alpha$ absorber (DLA) at redshift $z_{rm abs}=1.946$ towards two lensed images of the quasar J144254.78+405535.5 at redshift $z_{rm QSO} = 2.590$. The physical separation of the two lines of sight at the absorber redshift is $d_{rm abs}=0.7$~kpc based on our lens model. We observe absorption lines from neutral carbon and H$_2$ along both lines of sight indicating that cold gas is present on scales larger than $d_{rm abs}$. We measure column densities of HI to be $log N(rm H,i) = 20.27pm0.02$ and $20.34pm0.05$ and of H$_2$ to be $log N(rm H_2) = 19.7pm0.1$ and $19.9pm0.2$. The metallicity inferred from sulphur is consistent with Solar metallicity for both sightlines: $[{rm S/H}]_A = 0.0pm0.1$ and $[{rm S/H}]_B = -0.1pm0.1$. Based on the excitation of low rotational levels of H$_2$, we constrain the temperature of the cold gas phase to be $T=109pm20$ and $T=89pm25$ K for the two lines of sight. From the relative excitation of fine-structure levels of CI, we constrain the hydrogen volumetric densities in the range of $40-110$ cm$^{-3}$. Based on the ratio of observed column density and volumetric density, we infer the average individual `cloud size along the line of sight to be $lapprox0.1$ pc. Using the transverse line-of-sight separation of 0.7 kpc together with the individual cloud size, we are able to put an upper limit to the volume filling factor of cold gas of $f_{rm vol} < 0.2$ %. Nonetheless, the projected covering fraction of cold gas must be large (close to unity) over scales of a few kpc in order to explain the presence of cold gas in both lines of sight. Compared to the typical extent of DLAs (~10-30 kpc), this is consistent with the relative incidence rate of CI absorbers and DLAs.
We analyze the absorption and emission-line profiles produced by a set of simple, cool gas wind models motivated by galactic-scale outflow observations. We implement monte carlo radiative transfer techniques that track the propagation of scattered and fluorescent photons to generate 1D spectra and 2D spectral images. We focus on the MgII 2796,28303 doublet and FeII UV1 multiplet at ~2600A, but the results are applicable to other transitions that trace outflows (e.g. NaI, Lya, SiII). By design, the resonance transitions show blue-shifted absorption but one also predicts strong resonance and fine-structure line-emission at roughly the systemic velocity. This line-emission `fills-in the absorption reducing the equivalent width by up to 50%, shift the absorption-lin centroid by tens of km/s, and reduce the effective opacity near systemic. Analysis of cool gas outflows that ignores this line-emission may incorrectly infer that the gas is partially covered, measure asignificantly lower peak optical depth, and/or conclude that gas at systemic velocity is absent. Because the FeII lines are connected by optically-thin transitions to fine-structure levels, their profiles more closely reproduce the intrinsic opacity of the wind. Together these results naturally explain the absorption and emission-line characteristics observed for star-forming galaxies at z<1. We also study a scenario promoted to describe the outflows of z~3 Lyman break galaxies and find prfiles inconsistent with the observations due to scattered photon emission. Although line-emission complicates the analysis of absorption-line profiles, the surface brightness profiles offer a unique means of assessing the morphology and size of galactic-scale winds. Furthermore, the kinematics and line-ratios offer powerful diagnostics of outflows, motivating deep, spatially-extended spectroscopic observations.
We wish to study the extent and subparsec scale spatial structure of intervening quasar absorbers, mainly those involving neutral and molecular gas. We have selected quasar absorption systems with high spectral resolution and good S/N data, with some of their lines falling on quasar emission features. By investigating the consistency of absorption profiles seen for lines formed either against the quasar continuum source or on the much more extended emission line region (ELR), we can probe the extent and structure of the foreground absorber over the extent of the ELR (0.3-1 pc). The spatial covering analysis provides constraints on the transverse size of the absorber and thus is complementary to variability or photoionisation modelling studies. The methods we used to identify spatial covering or structure effects involve line profile fitting and curve of growth analysis.We have detected three absorbers with unambiguous non uniformity effects in neutral gas. For one extreme case, the FeI absorber at z_abs=0.45206 towards HE 0001-2340, we derive a coverage factor of the ELR of at most 0.10 and possibly very close to zero; this implies an absorber overall size no larger than 0.06 pc. For the z_abs=2.41837 CI absorber towards QSO J1439+1117, absorption is significantly stronger towards the ELR than towards the continuum source in several CI and CI* velocity components pointing to factors of about two spatial variations of their column densities and the presence of structures at the 100 au - 0.1 pc scale. The other systems with firm or possible effects can be described in terms of partial covering of the ELR, with coverage factors in the range 0.7 - 1. The overall results for cold, neutral absorbers imply a transverse extent of about five times or less the ELR size, which is consistent with other known constraints.
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