20 research outputs found

    Disk galaxies are self-similar: the universality of the HI-to-Halo mass ratio for isolated disks

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    Observed scaling relations in galaxies between baryons and dark matter global properties are key to shed light on the process of galaxy formation and on the nature of dark matter. Here, we study the scaling relation between the neutral hydrogen (HI) and dark matter mass in isolated rotationally-supported disk galaxies at low redshift. We first show that state-of-the-art galaxy formation simulations predict that the HI-to-dark halo mass ratio decreases with stellar mass for the most massive disk galaxies. We then infer dark matter halo masses from high-quality rotation curve data for isolated disk galaxies in the local Universe, and report on the actual universality of the HI-to-dark halo mass ratio for these observed galaxies. This scaling relation holds for disks spanning a range of 4 orders of magnitude in stellar mass and 3 orders of magnitude in surface brightness. Accounting for the diversity of rotation curve shapes in our observational fits decreases the scatter of the HI-to-dark halo mass ratio while keeping it constant. This finding extends the previously reported discrepancy for the stellar-to-halo mass relation of massive disk galaxies within galaxy formation simulations to the realm of neutral atomic gas. Our result reveals that isolated galaxies with regularly rotating extended HI disks are surprisingly self-similar up to high masses, which hints at mass-independent self-regulation mechanisms that have yet to be fully understood.Comment: 14 pages, 4 figures. Accepted for publication in ApJ

    Modelling the strongest silicate emission features of local type 1 AGN

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    We measure the 10 and 18ÎŒ18\mum silicate features in a sample of 67 local (z<0.1z<0.1) type 1 active galactic nuclei (AGN) with available {\it Spitzer} spectra dominated by non-stellar processes. We find that the 10ÎŒ10\mum silicate feature peaks at 10.3−0.9+0.7ÎŒ10.3^{+0.7}_{-0.9}\mum with a strength (Sip_{p} = ln fp_{p}(spectrum)/fp_{p}(continuum)) of 0.11−0.36+0.150.11^{+0.15}_{-0.36}, while the 18ÎŒ18\mum one peaks at 17.3−0.7+0.4ÎŒ17.3^{+0.4}_{-0.7}\mum with a strength of 0.14−0.06+0.060.14^{+0.06}_{-0.06}. We select from this sample sources with the strongest 10ÎŒ\mum silicate strength (σSi10ÎŒm>0.28\sigma_{Si_{10\mu m}}>0.28, 10 objects). We carry out a detailed modeling of the IRS/{\it Spitzer} spectra by comparing several models that assume different geometries and dust composition: a smooth torus model, two clumpy torus models, a two-phase medium torus model, and a disk+outflow clumpy model. We find that the silicate features are well modeled by the clumpy model of Nenkova et al. 2008, and among all models those including outflows and complex dust composition are the best (Hoenig et al. 2017). We note that even in AGN-dominated galaxies it is usually necessary to add stellar contributions to reproduce the emission at the shortest wavelengths.Comment: Accepted for publication in Ap

    Absence of nuclear polycyclic aromatic hydrocarbon emission from a compact starburst: the case of the type-2 quasar Mrk 477

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    Mrk 477 is the closest type-2 quasar, at a distance of 163 Mpc. This makes it an ideal laboratory for studying the interplay between nuclear activity and star formation with a great level of detail and signal-to-noise. In this Letter we present new mid-infrared (mid-IR) imaging and spectroscopic data with an angular resolution of 0.4″ (∌300 pc) obtained with the Gran Telescopio Canarias instrument CanariCam. The N-band (8–13 ÎŒm) spectrum of the central ∌400 pc of the galaxy reveals [S IV]λ10.51 ÎŒm emission, but no 8.6 or 11.3 ÎŒm polycyclic aromatic hydrocarbon (PAH) features, which are commonly used as tracers of recent star formation. This is in stark contrast with the presence of a nuclear starburst of ∌300 pc in size, an age of 6 Myr, and a mass of 1.1×108 M⊙, as constrained from ultraviolet Hubble Space Telescope observations. Considering this, we argue that even the more resilient, neutral molecules that mainly produce the 11.3 ÎŒm PAH band are most likely being destroyed in the vicinity of the active nucleus despite the relatively large X-ray column density, log NH = 23.5 cm−2, and modest X-ray luminosity, 1.5×1043 erg s−1. This highlights the importance of being cautious when using PAH features as star formation tracers in the central region of galaxies to evaluate the impact of feedback from active galactic nuclei

    The Galaxy Activity, Torus, and Outflow Survey (GATOS): III. Revealing the inner icy structure in local active galactic nuclei

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    We use JWST/MIRI MRS spectroscopy of a sample of six local obscured type 1.9/2 active galactic nuclei (AGN) to compare their nuclear mid-IR absorption bands with the level of nuclear obscuration traced by X-rays. This study is the first to use subarcsecond angular resolution data of local obscured AGN to investigate the nuclear mid-IR absorption bands with a wide wavelength coverage (4.9–28.1 ÎŒm). All the nuclei show the 9.7 ÎŒm silicate band in absorption. We compare the strength of the 9.7 and 18 ÎŒm silicate features with torus model predictions. The observed silicate features are generally well explained by clumpy and smooth torus models. We report the detection of the 6 ÎŒm dirty water ice band (i.e., a mix of water and other molecules such as CO and CO2) at subarcsecond scales (∌0.26″ at 6 ÎŒm; inner ∌50 pc) in a sample of local AGN with different levels of nuclear obscuration in the range log NHX-Ray (cm−2)∌22 − 25. We find good correlation between the 6 ÎŒm water ice optical depths and NHX-Ray. This result indicates that the water ice absorption might be a reliable tracer of the nuclear intrinsic obscuration in AGN. The weak water ice absorption in less obscured AGN (log NHX-ray (cm−2)â‰Č23.0 cm−2) might be related to the hotter dust temperature (> TsubH2O ∌ 110 K) expected to be reached in the outer layers of the torus due to their more inhomogeneous medium. Our results suggest it might be necessary to include the molecular content, such as H2O, aliphatic hydrocarbons (CH−), and more complex polycyclic aromatic hydrocarbon (PAH) molecules, in torus models to better constrain key parameters such as the torus covering factor (i.e., nuclear obscuration)

    The dust-gas AGN torus as constrained from X-ray and mid-infrared observations

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    Context. In recent decades, several multiwavelength studies have been dedicated to exploring the properties of the obscuring material in active galactic nuclei (AGN). Various models have been developed to describe the structure and distribution of this material and constrain its physical and geometrical parameters through spectral fitting techniques. However, questions around the way in which torus mid-infrared (mid-IR) and X-ray emission are related remain unanswered. Aims. In this work, we aim to study whether the dust continuum at mid-IR and gas reflection at X-rays have the same distribution in a sample of AGN. Methods. We carefully selected a sample of 36 nearby AGN with NuSTAR and Spitzer spectra available that satisfy the following criteria: (1) the AGN component dominates the mid-IR spectra (i.e., the stellar and interstellar medium components contribute less than 50% to the spectrum), and (2) the reflection component contributes significantly to the X-ray spectrum. Furthermore, we discarded the sources whose reflection component could be produced by ionized material in the disk. We derived the properties of the nuclear dust and gas through a spectral fitting, using models developed for mid-IR and X-ray wavelengths assuming smooth and clumpy distributions for this structure. Results. We find that a combination of smooth and clumpy distributions of gas and dust, respectively, is preferred for ∌80% of sources with good spectral fits according to the Akaike criterion. However, considering extra information about each individual source, such as the absorption variability, we find that ∌50% of our sources are best described by a clumpy distribution of both dust and gas. The remaining ∌50% of our sources can still be explained with a smooth distribution of gas and a clumpy distribution of dust. Furthermore, we explored the torus dust-to-gas ratio, finding that it is [0.01–1] times that of the interstellar medium. Conclusions. The results presented in this paper suggest that the distribution of the gas and dust in AGN is complex. We find at least six scenarios to explain the observed properties of our sample. In these scenarios, three gas–dust distribution combinations are possible: clumpy–clumpy, smooth–smooth, and smooth–clumpy. Most of them are in agreement with the notion that gas could also be located in the dust-free region, which is consistent with the dust-to-gas ratio found

    Observational hints on the torus obscuring gas behaviour through X-rays with NuSTAR data

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    According to theory, the torus of active galactic nuclei (AGN) is sustained from a wind coming off the accretion disc, and for low efficient AGN, it has been proposed that such structure disappears. However, the exact conditions for its disappearance remain unclear. This can be studied throughout the reflection component at X-rays, which is associated with distant and neutral material at the inner walls of the torus in obscured AGN. We select a sample of 81 AGNs observed with NuSTAR with a distance limit of D23⁠), with ∌20 per cent being Compton-thick. We also find an increase in the number of unobscured sources and a tentative increase on the ratio between FeKα emission line and Compton-hump luminosities toward λEdd=10−5⁠, suggesting that the contribution of the FeKα line changes with Eddington ratio. © 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical SocietyThis research has made use of the NASA/IPAC Extragalactic Data base (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made use of data and/or software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory. NOC would like to thank CONACyT scholarship No. 897887. CVC acknowledges support from CONACyT. We thank the UNAM PAPIIT project IN105720 (PI OGM). LHG acknowledges funds by ANID – Millennium Science Initiative Program – ICN12_009 awarded to the Millennium Institute of Astrophysics (MAS).With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.Peer reviewe
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