Impact of X-rays on CO emission from high-z galaxies

Abstract

We study the impact of active galactic nuclei (AGN) on the CO Spectral Line Energy Distribution (SLED) of high-$z$ galaxies. In particular, we want to assess if the CO SLED can be used as a probe of AGN activity. To this purpose, we develop a semi-analytical model that takes into account the radiative transfer and the clumpy structure of giant molecular clouds where the CO lines are excited, their distribution in the galaxy disk, and the torus obscuration of the AGN radiation. We study the joint effect on the CO SLED excitation of (i) the X-ray luminosity from the AGN ($L_X$), (ii) the size of the molecular disk, (iii) the inclination angle ($\Omega$) of the torus with respect to the molecular disk, and (iv) the GMC mean density. We also discuss the possibility of an enhanced Cosmic Ray Ionization Rate (CRIR). We find that the X-ray Dominated Region (XDR) generated by the AGN in every case enhances the CO SLED for $J>5$, with increasing excitation of high-$J$ CO lines for increasing X-ray luminosity. Because high-$z$ galaxies are compact, the XDR region typically encloses the whole disk, thus its effect can be more important with respect to lower redshift objects. The impact of the XDR can be disentangled from an enhanced CRIR either if $L_X>10^{44}\mathrm{erg}{\mathrm{s}}^{-1}$, or if $\Omega \ge 60^{\circ }$. We finally provide predictions on the CO(7-6)/[CII] and CO(17-16)/[CII] ratios as a function of $L_X$, which can be relevant for ALMA follow up of galaxies and quasars previously detected in [CII].

accepted for publication in MNRAS

References in corpus (35)

• Theory of Star Formation
• An Observational Determination of the Bolometric Quasar Luminosity Function
• On the Star Formation Efficiency of Turbulent Magnetized Clouds
• Diagnostics of irradiated dense gas in galaxy nuclei. II. A grid of XDR and PDR models
• H3+ in Diffuse Interstellar Clouds: a Tracer for the Cosmic-Ray Ionization Rate
• Galaxy growth in a massive halo in the first billion years of cosmic history
• Highly-excited CO emission in APM08279+5255 at z=3.9
• A Massive Molecular Gas Reservoir in the z=5.3 Submillimeter Galaxy AzTEC-3
• The Herschel Comprehensive (U)LIRG Emission Survey (HerCULES): CO Ladders, fine structure lines, and neutral gas cooling
• Tracing the reionization epoch with ALMA: [CII] emission in z~7 galaxies
• Star formation and the interstellar medium in z>6 UV-luminous Lyman-break galaxies
• ISM properties of a Massive Dusty Star-Forming Galaxy discovered at z ~ 7
• Effective destruction of CO by cosmic rays: implications for tracing H${}_2$ gas in the Universe
• Deep into the structure of the first galaxies: SERRA views
• Radial distribution of dust, stars, gas, and star-formation rate in DustPedia face-on galaxies
• Zooming on the internal structure of $z\simeq 6$ galaxies
• The impact of chemistry on the structure of high-z galaxies
• Evolution of column density distributions within Orion~A
• The compact, ~1 kpc host galaxy of a quasar at z=7.1
• Kinematics of $z\ge 6$ galaxies from [CII] line emission
• ALMA reveals metals yet no dust within multiple components in CR7
• Molecular gas in three z~7 quasar host galaxies
• CO line emission from galaxies in the Epoch of Reionization
• Molecular gas in QSO host galaxies at z>5
• High-J CO SLEDs in nearby infrared bright galaxies observed by Herschel-PACS
• Spatially Resolved Interstellar Medium and Highly-Excited Dense Molecular Gas in the Most Luminous Quasar at z=6.327
• Models of irradiated molecular shocks
• First CO(17-16) emission line detected in a z > 6 quasar
• Quasar outflows at $z\ge 6$: the impact on the host galaxies
• Galaxy evolution studies with the SPace IR telescope for Cosmology and Astrophysics (SPICA): the power of IR spectroscopy
• On the fidelity of the core mass functions derived from dust column density data
• CO excitation in the Seyfert galaxy NGC 34: stars, shock or AGN driven?
• Galaxy Formation Through Filamentary Accretion at z=6.1
• CO excitation in the Seyfert galaxy NGC7130
• X-ray spectroscopy of the z=6.4 quasar J1148+5251

Cited by in corpus (27)

• Photodissociation and X-Ray Dominated Regions
• Supermassive Black Holes at High Redshift are Expected to be Obscured by their Massive Host Galaxies' Inter Stellar Medium
• A survey of high-$z$ galaxies: SERRA simulations
• High molecular gas content and star formation rates in local galaxies that host quasars, outflows and jets
• An ALMA multi-line survey of the ISM in two quasar host-companion galaxy pairs at $z>6$
• The ALMA-ALPAKA survey I: high-resolution CO and [CI] kinematics of star-forming galaxies at z = 0.5-3.5
• Molecular gas in z~6 quasar host galaxies
• AGN impact on the molecular gas in galactic centers as probed by CO lines
• PDFchem: A new fast method to determine ISM properties and infer environmental parameters using probability distributions
• Bright Extragalactic ALMA Redshift Survey (BEARS) III: Detailed study of emission lines from 71 Herschel targets
• The effect of active galactic nuclei on the cold interstellar medium in distant star-forming galaxies
• An ALMA view of 11 Dusty Star Forming Galaxies at the peak of Cosmic Star Formation History
• Unusually high HCO+/CO ratios in and outside supernova remnant W49B
• Big Three Dragons: Molecular Gas in a Bright Lyman-Break Galaxy at $z=7.15$
• The cold molecular gas in z$\gtrsim$6 quasar host galaxies
• The molecular gas in the central region of NGC 7213
• Molecular gas excitation and outflow properties of obscured quasars at z$\sim$0.1
• Spritz is sparkling: simulated CO and [CII] luminosities
• A possible relation between global CO excitation and massive molecular outflows in local ULIRGs
• Warm Gas in the Vicinity of a Supermassive Black hole 13 Billion Years Ago
• Deep kiloparsec view of the molecular gas in a massive star-forming galaxy at cosmic noon
• Probing the heating of the neutral atomic interstellar medium in the Dwarf Galaxy Survey through infrared cooling lines
• SIGAME v3: Gas Fragmentation in Post-processing of Cosmological Simulations for More Accurate Infrared Line Emission Modeling
• ALMA High-J CO Spectroscopy of High-Redshift Galaxies. II. 0.03" Resolution CO Kinematics Reveal Super-Eddington Accretion in a Dust-Obscured Galaxy at z=3.111
• ALMA survey of a massive node of the Cosmic Web at $z\sim 3$. II. A dynamically cold and massive disk galaxy in the proximity of a hyperluminous quasar
• Predicting the resolved CO emission of $z=1-3$ star-forming galaxies
• Direct detection of cool molecular gas in a star-forming galaxy at $z=7.31$