arXiv subjects

D. Rigopoulou

Publications and source records attributed to D. Rigopoulou.

At least 55 records · Page 3Linked to original sources

arXiv2021

Polycyclic Aromatic Hydrocarbons in Seyfert and star-forming galaxies

Polycyclic Aromatic Hydrocarbons (PAHs) are carbon-based molecules resulting from the union of aromatic rings and related species, which are likely responsible for strong infrared emission features (3.3, 6.2, 7.7, 8.6, 11.3 and 12.7 microns). In this work, using a sample of 50 Seyfert galaxies (DL<100 Mpc) we compare the circumnuclear (inner kpc) PAH emission of AGN to that of a control sample of star-forming galaxies (22 luminous infrared galaxies and 30 HII galaxies), and investigate the differences between central and extended PAH emission. Using Spitzer/InfraRed Spectrograph spectral data of Seyfert and star-forming galaxies and newly developed PAH diagnostic model grids, derived from theoretical spectra, we compare the predicted and observed PAH ratios. We find that star-forming galaxies and AGN-dominated systems are located in different regions of the PAH diagnostic diagrams. This suggests that not only are the size and charge of the PAH molecules different, but also the nature and hardness of the radiation field that excite them. We find tentative evidence that PAH ratios in AGN-dominated systems are consistent with emission from larger PAH molecules (Nc>300-400) as well as neutral species. By subtracting the spectrum of the central source from the total, we compare the PAH emission in the central vs extended region of a small sample of AGN. In contrast to the findings for the central regions of AGN-dominated systems, the PAH ratios measured in the extended regions of both type 1 and type 2 Seyfert galaxies can be explained assuming similar PAH molecular size distribution and ionized fractions of molecules to those seen in central regions of star-forming galaxies (100<Nc<300).

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arXiv2021

The Galaxy Activity, Torus and Outflow Survey (GATOS): II. Torus and polar dust emission in nearby Seyfert galaxies

We compare mid-IR and ALMA far-IR images of 12 nearby Seyferts selected from GATOS. The mid-IR unresolved emission contributes more than 60% of the nuclear emission in most galaxies. By contrast, the ALMA 870micron continuum emission is mostly resolved and typically along the torus equatorial direction (Paper I, Garcia-Burillo et al. 2021). The Eddington ratios and nuclear hydrogen column densities NH of half the sample are favorable to launching polar and/or equatorial dusty winds, according to simulations. Six show mid-IR extended emission in the polar direction as traced by the NLR and perpendicular to the ALMA emission. In a few, the nuclear NH might be too high to uplift large quantities of dusty material along the polar direction. Five galaxies have low NH and/or Eddington ratios and thus polar dusty winds are not likely. We generate new CAT3D-WIND disk-wind model images. At low wind-to-disk cloud ratios the far-IR model images have disk- and ring-like morphologies. The X-shape associated with dusty winds is seen better in the far-IR at intermediate-high inclinations for the extended-wind configurations. In most models, the mid-IR emission comes from the inner part of the disk/cone. Extended bi-conical and one-sided polar mid-IR emission is seen in extended-wind configurations and high wind-to-disk cloud ratios. When convolved to our resolution, the model images reproduce qualitative aspects of the observed morphologies. Low-intermediate wind-to-disk ratios are required to account for the large fractions of unresolved mid-IR emission. This work and Paper I provide observational support for the torus+wind scenario. The wind component is more relevant at high Eddington ratios and/or AGN luminosities, and polar dust emission is predicted at NH of up to $10^{24}$cm$^{-2}$. The torus/disk component, on the other hand, prevails at low luminosities and/or Eddington ratios. (Abridged)

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arXiv2021

The Galaxy Activity, Torus and Outflow Survey (GATOS) I. ALMA images of dusty molecular tori in Seyfert galaxies

We present the first results of the Galaxy Activity, Torus and Outflow Survey (GATOS), a project aimed at understanding the properties of the dusty molecular tori and their connection to the host galaxy in nearby Seyfert galaxies. Our project expands the range of AGN luminosities and Eddington ratios covered by previous surveys of Seyferts conducted by ALMA and allows us to study the gas feeding and feedback cycle in a combined sample of 19 Seyferts. We used ALMA to obtain new images of the emission of molecular gas and dust using the CO(3-2) and HCO+(4-3) lines as well as their underlying continuum emission at 870 microns with high spatial resolutions (0.1'' ~ 7 - 13 pc) in the CND of 10 nearby (D < 28 Mpc) Seyfert galaxies. Our new ALMA observations detect 870 micron continuum and CO line emission from spatially resolved disks located around the AGN in all the sources. The bulk of the continuum flux can be accounted for by thermal emission from dust in the majority of the targets. For most of the sources the disks show a preponderant orientation perpendicular to the AGN wind axes, as expected for dusty molecular tori. The median diameters and molecular gas masses of the tori are ~ 42 pc, and ~ 6 x 10**5 Msun, respectively. We find a positive correlation between the line-of-sight gas column densities responsible for the absorption of X-rays and the molecular gas column densities derived from CO towards the AGN in our sources. The radial distributions of molecular gas in the CND of our combined sample show signs of nuclear-scale molecular gas deficits. We also detect molecular outflows in the sources that show the most extreme nuclear-scale gas deficits in our sample. These observations find for the first time supporting evidence that the imprint of AGN feedback is more extreme in higher luminosity and/or higher Eddington ratio Seyfert galaxies.

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arXiv2021

Are local ULIRGs powered by AGN? The sub-kpc view of the 220 GHz continuum. PUMA II

We analyze high-resolution (400pc) 220GHz continuum and CO(2-1) ALMA observations of a representative sample of 23 local (z<0.165) ULIRG systems (34 individual nuclei) as part of the "Physics of ULIRGs with MUSE and ALMA" (PUMA) project. The deconvolved half-light radii of the 220GHz continuum sources are between <60-350 pc (median 90pc). We associate these regions with the regions emitting the bulk of the infrared luminosity. The good agreement, within a factor of 2, between the 220GHz fluxes and the extrapolation of the infrared gray-body, and the small synchrotron and free-free contributions support this assumption. The cold molecular gas emission sizes, r_CO, are 60-700 pc and are similar in advanced mergers and early interacting systems. On average, r_CO are 2.5 times larger than the continuum. We derive L_IR and cold molecular gas surface densities: log Sigma(L_IR)=11.5-14.3 Lsun/kpc^2 and log Sigma(H2)=2.9-4.2 Msun/pc^2. Assuming that the L_IR is produced by star-formation, this corresponds to median Sigma(SFR)=2500 Msun/yr/kpc^2 which would imply extremely short depletion times, <1-15 Myr, and unphysical SF efficiencies >1 for 70% of the sample. Therefore, this favors the presence of obscured AGN that could dominate the L_IR. We also classify the ULIRG nuclei in two groups: (a) compact nuclei (r<130 pc) with high mid-IR excess emission found in optically classified AGN; and (b) nuclei following a relation with decreasing mid-IR excess for decreasing r. 60% of the interacting nuclei lie in the low end (<130 pc) of this relation, while only 30% of the advanced mergers do so, suggesting that in the early interaction phases the activity occurs in more compact and obscured regions. About two thirds of the nuclei are above the Eddington limit which is consistent with the detection of massive outflows in local ULIRGs and the potential role of radiation pressure in the launching process.

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arXiv2021

A Complete 16 micron-Selected Galaxy Sample at $z\sim1$: Mid-infrared Spectral Energy Distributions

We describe a complete, flux-density-limited sample of galaxies at redshift $0.8 < z < 1.3$ selected at 16 micron. At the selection wavelength near 8 micron rest, the observed emission comes both from dust heated by intense star formation and from active galactic nuclei (AGNs). Fitting the spectral energy distributions (SEDs) of the sample galaxies to local-galaxy templates reveals that more than half the galaxies have SEDs dominated by star formation. About one sixth of the galaxy SEDs are dominated by an AGN, and nearly all the rest of the SEDs are composite. Comparison with X-ray and far-infrared observations shows that combinations of luminosities at rest-frame 4.5 and 8 micron give good measures of both AGN luminosity and star-formation rate. The sample galaxies mostly follow the established star-forming main sequence for $z=1$ galaxies, but of the galaxies more than 0.5 dex above that main sequence, more than half have AGN-type SEDs. Similarly, the most luminous AGNs tend to have higher star-formation rates than the main sequence value. Galaxies with stellar masses $>$10$^{11}$\,\Msun\ are unlikely to host an AGN. About 1% of the sample galaxies show an SED with dust emission typical of neither star formation nor an AGN.

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arXiv2020

Origins Space Telescope: From First Light to Life -- ESA Voyage 2050 White Paper

The Origins Space Telescope (Origins) is one of four science and technology definition studies selected by National Aeronautics and Space Administration (NASA) in preparation of the 2020 Astronomy and Astrophysics Decadal survey in the US. Origins will trace the history of our origins from the time dust and heavy elements permanently altered the cosmic landscape to present-day life. It is designed to answer three major science questions: How do galaxies form stars, make metals, and grow their central supermassive black holes from reionization? How do the conditions for habitability develop during the process of planet formation? Do planets orbiting M-dwarf stars support life? Origins operates at mid- to far-infrared wavelengths from ~2.8 to 588 μm, is more than 1000 times more sensitive than prior far-IR missions due to its cold (~4.5 K) aperture and state-of-the-art instruments.

astro-ph.IM↗

arXiv2020

Multi-phase feedback processes in the Sy2 galaxy NGC 5643

We study the multi-phase feedback processes in the central ~3 kpc of the barred Sy 2 galaxy NGC 5643. We use observations of the cold molecular gas (ALMA CO(2-1)) and ionized gas (MUSE IFU). We study different regions along the outflow zone which extends out to ~2.3 kpc in the same direction (east-west) as the radio jet, as well as nuclear/circumnuclear regions in the host galaxy disk. The deprojected outflowing velocities of the cold molecular gas (median Vcentral~189 km s^-1) are generally lower than those of the outflowing ionized gas, which reach deprojected velocities of up to 750 km s^-1 close to the AGN, and their spatial profiles follow those of the ionized phase. This suggests that the outflowing molecular gas in the galaxy disk is being entrained by the AGN wind. We derive molecular and ionized outflow masses of ~5.2x10^7 Msun and 8.5x10^4 Msun and molecular and ionized outflow mass rates of ~51 Msun yr^-1 and 0.14 Msun yr^-1. Therefore, the molecular phase dominates the outflow mass and outflow mass rate, while the outflow kinetic power and momentum are similar in both phases. However, the wind momentum load for the molecular and ionized outflow phases are ~27-5 and <1, which suggests that the molecular phase is not momentum conserving while the ionized one most certainly is. The molecular gas content (~1.5x10^7 Msun) of the eastern spiral arm is approximately 50-70% of the content of the western one. We interpret this as destruction/clearing of the molecular gas produced by the AGN wind impacting in the host galaxy. The increase of the molecular phase momentum implies that part of the kinetic energy from the AGN wind is transmitted to the molecular outflow. This suggest that in Sy-like AGN such as NGC 5643, the radiative/quasar and the kinetic/radio AGN feedback modes coexist and may shape the host galaxies even at kpc-scales via both positive and (mild) negative feedback.

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arXiv2020

Excitation and acceleration of molecular outflows in LIRGs: The extended ESO 320-G030 outflow on 200-pc scales

We used high-spatial resolution (70 pc; 0.3") CO multi-transition (1-0, 2-1, 4-3, and 6-5) ALMA data to study the physical conditions and kinematics of the cold molecular outflow in the local LIRG ESO320-G030 (d=48 Mpc, log LIR/Lsun=11.3). ESO320-G030 is a double-barred isolated spiral, but its compact and obscured nuclear starburst (SFR~15 Msun/yr; Av~40 mag) resembles those of more luminous ULIRGs. In the outflow, the 1-0/2-1 ratio is enhanced with respect to the rest of the galaxy and the CO(4-3) transition is undetected. This indicates that the outflowing molecular gas is less excited than the gas in the nuclear starburst (launching site) and the galaxy disk. Non-LTE radiative transfer modeling reveals that the properties of the outflow molecular clouds differ from those of the nuclear and disk clouds: The kinetic temperature is lower (~9 K) in the outflow, and the outflowing clouds have lower column densities. Assuming a 10^-4 CO abundance, the large internal velocity gradients, 60^+250_-45 km/s/pc, imply that the outflowing molecular clouds are not bound by self-gravity. All this suggests that the life-cycle (formation, collapse, dissipation) of the disk clouds might differ from that of the outflowing clouds which might not be able to form stars. The low Tkin of the molecular outflow remains constant up to 1.7 kpc. This indicates that the heating by the hotter ionized outflow phase is not efficient and may favor the survival of the outflow molecular phase. The velocity structure of the outflow shows a 0.8 km/s/pc velocity gradient between 190-560 pc and then a constant maximum velocity (~750 km/s) up to 1.7 kpc. This is compatible with a pure gravitational evolution of the outflow under certain mass outflow rate and launching velocity variations. Alternatively, ram pressure acceleration and cloud evaporation could explain the observed kinematics and size of the molecular phase.

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arXiv2020

Cold molecular gas and PAH emission in Seyfert galaxies

We investigate the relation between the detection of the $11.3\,μ$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 $11.3\,μ$m PAH feature contain more cold molecular gas (median $1.6\times 10^7\,M_\odot$) 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 $11.3\,μ$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.

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arXiv2020

Dust and gas content of high-redshift galaxies hosting obscured AGN in the CDF-S

Obscured AGN represent a significant fraction of the entire AGN population, especially at high redshift (~70% at z=3--5). They are often characterized by the presence of large gas and dust reservoirs that are thought to sustain and possibly obscure vigorous star formation processes that make these objects shine at far-IR and sub-mm wavelengths. We exploit ALMA Cycle 4 observations of the continuum (~2.1mm) and high-J CO emission of a sample of six X-ray selected SMGs hosting an obscured AGN at z_spec>2.5 in the 7 Ms CDF-S. We measured the masses and sizes of the dust and molecular gas and we derived the gas density and column density on the basis of a uniform sphere geometry. Finally, we compared the measured column densities with those derived from the Chandra X-ray spectra. We detected both the continuum and line emission for three sources for which we measured both the flux density and size. For the undetected sources, we derived an upper limit on the flux density. We found that the detected galaxies are rich in gas and dust (molecular gas mass in the range <0.5 - 2.7 x 10^10 M_sun for α_CO=0.8 and up to ~2 x 10^11~M_sun for α_CO=6.5, and dust mass <0.9 - 4.9 x 10^8 M_sun) and compact (gas major axis 2.1-3.0 kpc, dust major axis 1.4-2.7 kpc). The column densities associated with the ISM are on the order of 10^(23-24) cm-2, which is comparable with those derived from the X-ray spectra. For the detected sources we also derived dynamical masses in the range 0.8 - 3.7 x 10^10 M_sun. We conclude that the ISM of high redshift galaxies can substantially contribute to nuclear obscuration up to the Compton-thick (>10^24 cm-2) regime. In addition, we found that all the detected sources show a velocity gradient reminding one rotating system, even though two of them show peculiar features in their morphology that can be associated with a chaotic, possibly merging, structure.

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arXiv2020

Searching for molecular gas in/outflows in the nuclear regions of five Seyfert galaxies

AGN-driven outflows are believed to play an important role in regulating the growth of galaxies mostly via negative feedback. However, their effects on their hosts are far from clear, especially for low and moderate luminosity Seyferts. To investigate this issue, we have obtained cold molecular gas observations, traced by the CO(2-1) transition, using the NOEMA interferometer of five nearby (distances between 19 and 58 Mpc) Seyfert galaxies. The resolution of approx. 0.3-0.8 arcsec (approx. 30-100 pc) and field of view of NOEMA allowed us to study the CO(2-1) morphology and kinematics in the nuclear regions (approx. 100 pc) and up to radial distances of approx. 900 pc. We have detected CO(2-1) emission in all five galaxies with disky or circumnuclear ring like morphologies. We derived cold molecular gas masses on nuclear (approx. 100 pc) and circumnuclear (approx. 650 pc) scales in the range from $10^6$ to $10^7$M$_{\odot}$ and from $10^7$ to $10^8$ $M_{\odot}$, respectively. In all of our galaxies the bulk of this gas is rotating in the plane of the galaxy. However, non-circular motions are also present. In NGC 4253, NGC 4388 and NGC 7465, we can ascribe the streaming motions to the presence of a large-scale bar. In Mrk 1066 and NGC 4388, the non-circular motions in the nuclear regions are explained as outflowing material due to the interaction of the AGN wind with molecular gas in the galaxy disk. We conclude that for an unambiguous and precise interpretation of the kinematics of the cold molecular gas we need a detailed knowledge of the host galaxy (i.e., presence of bars, interactions, etc) as well as of the ionized gas kinematics and the ionization cone geometry.

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arXiv2019

Discovery of a giant and luminous Lya+CIV+HeII nebula at z=3.326 with extreme emission line ratios

We present the discovery of HLock01-LAB, a luminous and large Lya nebula at z=3.326. Medium-band imaging and long-slit spectroscopic observations with the Gran Telescopio Canarias reveal extended emission in the Lya 1215Å, CIV1550Å, and HeII 1640Ålines over ~100kpc, and a total luminosity L(Lya)=(6.4+/-0.1)x10^44 erg s^-1. HLock01-LAB presents an elongated morphology aligned with two faint radio sources contained within the central ~8kpc of the nebula. The radio structures are consistent to be faint radio jets or lobes of a central galaxy, whose spectrum shows nebular emission characteristic of a type-II active galactic nucleus (AGN). The continuum emission of the AGN at short wavelengths is, however, likely dominated by stellar emission of the host galaxy, for which we derive a stellar mass M* = 2.3x10^11 Msun. The detection of extended emission in CIV and CIII] indicates that the gas within the nebula is not primordial. Feedback may have enriched the halo at at least 50 kpc from the nuclear region. Using rest-frame UV emission-line diagnostics, we find that the gas in the nebula is likely heated by the AGN. Nevertheless, at the center of the nebula we find extreme emission line ratios of Lya/CIV~60 and Lya/HeII~80, one of the highest values measured to date, and well above the standard values of photoionization models (Lya/HeII~30 for case B photoionization). Our data suggest that jet-induced shocks are likely responsible for the increase of the electron temperature and, thus, the observed Lya enhancement in the center of the nebula. This scenario is further supported by the presence of radio structures and perturbed kinematics in this region. The large Lya luminosity in HLock01-LAB is likely due to a combination of AGN photoionization and jet-induced shocks, highlighting the diversity of sources of energy powering Lya nebulae. [abridged]

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arXiv2019

A nuclear molecular outflow in the Seyfert galaxy NGC3227

We present ALMA observations of the CO(2-1) and CO(3-2) molecular gas transitions and associated (sub)-mm continua of the nearby Seyfert 1.5 galaxy NGC3227 with angular resolutions 0.085-0.21" (7-15pc). On large scales the cold molecular gas shows circular motions as well as streaming motions on scales of a few hundred parsecs associated with a large scale bar. We fitted the nuclear ALMA 1.3mm emission with an unresolved component and an extended component. The 850$μ$m emission shows at least two extended components, one along the major axis of the nuclear disk and the other along the axis of the ionization cone. The molecular gas in the central region (1" ~73pc) shows several CO clumps with complex kinematics which appears to be dominated by non-circular motions. While we cannot demonstrate conclusively the presence of a warped nuclear disk, we also detected non-circular motions along the kinematic minor axis. They reach line-of-sight velocities of v-vsys =150-200km/s. Assuming that the radial motions are in the plane of the galaxy, then we interpret them as a nuclear molecular outflow due to molecular gas in the host galaxy being entrained by the AGN wind. We derive molecular outflow rates of $5\,M_\odot\,{\rm yr}^{-1}$ and $0.6\,M_\odot\,{\rm yr}^{-1}$ at projected distances of up to 30pc to the northeast and southwest of the AGN, respectively. At the AGN location we estimate a mass in molecular gas of $5\times 10^{5}\,M_\odot$ and an average column density $N({\rm H}_2) = 2-3\times 10^{23}\,{\rm cm}^{-2}$ in the inner 15pc. The nuclear molecular gas and sub-mm continuum emission of NGC3227 do not resemble the classical compact torus. Rather, these emissions extend for several tens of parsecs and appear connected with the circumnuclear ring in the host galaxy disk, as found in other local AGN. (Abridged)

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arXiv2019

Optical integral field spectroscopy of intermediate redshift infrared bright galaxies

The extreme infrared (IR) luminosity of local luminous and ultra-luminous IR galaxies (U/LIRGs; 11 < log LIR /Lsun < 12 and log LIR /Lsun > 12, respectively) is mainly powered by star-formation processes triggered by mergers or interactions. While U/LIRGs are rare locally, at z > 1, they become more common, they dominate the star-formation rate (SFR) density, and a fraction of them are found to be normal disk galaxies. Therefore, there must be an evolution of the mechanism triggering these intense starbursts with redshift. To investigate this evolution, we present new optical SWIFT integral field spectroscopic Hα+[NII] observations of a sample of 9 intermediate-z (0.2 < z < 0.4) U/LIRG systems selected from Herschel 250μm observations. The main results are the following: (a) the ratios between the velocity dispersion and the rotation curve amplitude indicate that 10-25% (1-2 out of 8) might be compatible with being isolated disks while the remaining objects are interacting/merging systems; (b) the ratio between un-obscured and obscured SFR traced by Hα and LIR, respectively, is similar in both local and these intermediate-z U/LIRGs; and (c) the ratio between 250μm and the total IR luminosities of these intermediate-z U/LIRGs is higher than that of local U/LIRGs with the same LIR . This indicates a reduced dust temperature in these intermediate-z U/LIRGs. This, together with their already measured enhanced molecular gas content, suggests that the interstellar medium conditions are different in our sample of intermediate-z galaxies when compared to local U/LIRGs.

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arXiv2018

PAHs as tracers of the molecular gas in star-forming galaxies

[Abridged] We combine new CO(1-0) line observations of 24 intermediate redshift galaxies (0.03 < z < 0.28) along with literature data of galaxies at 0<z<4 to explore scaling relations between the dust and gas content using PAH 6.2 $μ$m ($L_{6.2}$), CO ($L'_{\rm CO}$), and infrared ($L_{\rm IR}$) luminosities for a wide range of redshifts and physical environments. Our analysis confirms the existence of a universal $L_{6.2}-L_{\rm CO}$ correlation followed by normal star-forming galaxies (SFGs) and starbursts (SBs) at all redshifts. This relation is also followed by local ULIRGs that appear as outliers in the $L_{6.2}-L_{\rm IR}$ and $L_{\rm IR}-L'_{\rm CO}$ relations from the sequence defined by normal SFGs. The emerging tight ($σ\approx 0.26$ dex) and linear ($α= 1.03$) relation between $L_{6.2}$ and $L_{\rm CO}$ indicates a $L_{6.2}$ to molecular gas ($M_{\rm H_2}$) conversion factor of $α_{6.2} = M_{\rm H2}/L_{6.2} = (2.7\pm1.3) \times α_{\rm CO}$, where $α_{\rm CO}$ is the $L'_{\rm CO}$ to $M_{\rm H_2}$ conversion factor. We also find that on galaxy integrated scales, PAH emission is better correlated with cold rather than with warm dust emission, suggesting that PAHs are associated with the diffuse cold dust, which is another proxy for $M_{\rm H_2}$. Focusing on normal SFGs among our sample, we employ the dust continuum emission to derive $M_{\rm H_2}$ estimates and find a constant $M_{\rm H_2}/L_{6.2}$ ratio of $α_{6.2} = 12.3 \ M_{\rm H_2}/{\rm L}_{\odot}$ ($σ\approx 0.3$ dex). We propose that the presented $L_{6.2}-L'_{\rm CO}$ and $L_{6.2}-M_{\rm H_2}$ relations will serve as useful tools for the determination of the physical properties of high-$z$ SFGs, for which PAH emission will be routinely detected by the James Webb Space Telescope.

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arXiv2018

Resolving the nuclear obscuring disk in the Compton-thick Seyfert galaxy NGC5643 with ALMA

We present ALMA Band 6 $^{12}$CO(2--1) line and rest-frame 232GHz continuum observations of the nearby Compton-thick Seyfert galaxy NGC5643 with angular resolutions 0.11-0.26arcsec (9-21pc). The CO(2--1) integrated line map reveals emission from the nuclear and circumnuclear region with a two-arm nuclear spiral extending 10arcsec on each side. The circumnuclear CO(2--1) kinematics can be fitted with a rotating disk, although there are regions with large residual velocities and/or velocity dispersions. The CO(2--1) line profiles of these regions show two different velocity components. One is ascribed to the circular component and the other to the interaction of the AGN outflow, as traced by the [O III]5007AA emission, with molecular gas in the disk a few hundred parsecs from the AGN. On nuclear scales, we detected an inclined CO(2--1) disk (diameter 26 pc, FWHM) oriented almost in a north-south direction. The CO(2--1) nuclear kinematics can be fitted with a rotating disk which appears to be tilted with respect to the large scale disk. There are strong non-circular motions in the central 0.2-0.3 arcsec with velocities of up to 110km/s. In the absence of a nuclear bar, these motions could be explained as radial outflows in the nuclear disk. We estimate a total molecular gas mass for the nuclear disk of $M({\rm H}_2)=1.1\times 10^7\,M_\odot$ and an H$_2$ column density toward the location of the AGN of $N({\rm H}_2)\sim 5 \times 10^{23}\,{\rm cm}^{-2}$, for a standard CO-to-H$_2$ conversion factor. We interpret this nuclear molecular gas disk as the obscuring torus of NGC5643 as well as the collimating structure of the ionization cone.

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arXiv2018

Spatially resolved cold molecular outflows in ULIRGs

We present new CO(2-1) observations of 3 low-z (~350 Mpc) ULIRG systems (6 nuclei) observed with ALMA at high-spatial resolution (~500 pc). We detect massive cold molecular gas outflows in 5 out of 6 nuclei (0.3-5)x10^8 Msun. These outflows are spatially resolved with deprojected radii of 0.25-1 kpc although high-velocity molecular gas is detected up to ~0.5-1.8 kpc (1-6 kpc deprojected). The mass outflow rates are 12-400 Msun/yr and the inclination corrected average velocity of the outflowing gas 350-550 km/s (v_max = 500-900 km/s). The origin of these outflows can be explained by the nuclear starbursts although the contribution of an obscured AGN can not be completely ruled out. The position angle (PA) of the outflowing gas along the kinematic minor axis of the nuclear molecular disk suggests that the outflow axis is perpendicular to the disk for three of these outflows. Only in one case, the outflow PA is clearly not along the kinematic minor axis. The outflow depletion times are 15-80 Myr which are slightly shorter than the star-formation (SF) depletion times (30-80 Myr). However, we estimate that only 15-30% of the outflowing gas will escape the gravitational potential of the nucleus. The majority of the outflowing gas will return to the disk after 5-10 Myr and become available to form new stars. Therefore, these outflows will not likely quench the nuclear starbursts. These outflows would be consistent with being driven by radiation pressure (momentum-driven) only if the coupling between radiation and dust increases with increasing SF rates. This can be achieved if the dust optical depth is higher in objects with higher SF. The relatively small sizes (<1 kpc) and dynamical times (<3 Myr) of the cold molecular outflows suggests that molecular gas cannot survive longer in the outflow environment or that it cannot form efficiently beyond these distances or times. (Abridged)

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arXiv2017

HERUS: The Far-IR/Submm Spectral Energy Distributions of Local ULIRGs & Photometric Atlas

We present the Herschel-SPIRE photometric atlas for a complete flux limited sample of 43 local Ultraluminous Infrared Galaxies (ULIRGs), selected at 60$μ$m by IRAS, as part of the HERschel ULIRG Survey (HERUS). Photometry observations were obtained using the SPIRE instrument at 250, 350 and 500$μ$m. We describe these observations, present the results, and combine the new observations with data from IRAS to examine the far-IR spectral energy distributions (SEDs) of these sources. We fit the observed SEDs of HERUS objects with a simple parameterised modified black body model where temperature and emissivity $β$ are free parameters. We compare the fitted values to those of non-ULIRG local galaxies, and find, in agreement with earlier results, that HERUS ULIRGs have warmer dust (median temperature T = 37.9+/-4.7 K compared to 21.3+/-3.4 K) but a similar $β$ distribution (median $β$ = 1.7 compared to 1.8) to the Herschel reference sample (HRS, Cortese et al., 2014) galaxies. Dust masses are found to be in the range of 10^7.5 to 10^9 Msun significantly higher than that of Herschel Reference Sample (HRS) sources. We compare our results for local ULIRGs with higher redshift samples selected at 250 and 850$μ$m. These latter sources generally have cooler dust and/or redder 100-to-250 $μ$m colours than our 60$μ$m-selected ULIRGs. We show that this difference may in part be the result of the sources being selected at different wavelengths rather than being a simple indication of rapid evolution in the properties of the population.

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