arXiv subjects

K. M. Dasyra

Publications and source records attributed to K. M. Dasyra.

At least 19 recordsLinked to original sources

arXiv2026

Wild is the wind from low-luminosity AGN: A jet-driven gas bubble blowing out a massive CO-dark outflow in ESO 420-G13

We present JWST/MIRI mid-infrared integral field spectroscopy combined with ALMA CO(2-1) observations of the post-starburst galaxy ESO 420-G13, hosting a low-luminosity AGN. The unprecedented spatial and spectral resolution of MIRI enables a detailed study of the molecular and ionised gas kinematics, excitation, and energetics in the nuclear kiloparsec, revealing the impact of AGN feedback in a system with modest radiative output. Despite its faint radio and X-ray emission ($L_{2-10keV} \sim 10^{40}$ erg/s), ESO 420-G13 exhibits powerful kinetic feedback in the form of massive molecular and ionised gas outflows, with a total kinetic power of $\sim 1.4 \times 10^{41}$ erg/s. This corresponds to a jet-ISM coupling efficiency of ~3.8%, within the range observed in more powerful AGN. The feedback is driven by a previously undetected compact jet, traced by collimated coronal-line and extended X-ray emission to >870 pc from the nucleus. The interaction is strongest ~370 pc north of the nucleus, where a fast ionised gas stream emerges perpendicular to the jet axis, coinciding with a bend in the jet direction. Enhanced velocity dispersion in warm H$_2$ surrounds this gas stream, consistent with an expanding molecular bubble. Massive molecular outflows are detected at its edges; the blueshifted outflow is devoid of CO emission, likely due to CO destruction in shocks or by cosmic rays from the jet-ISM interaction. About 5% of the central molecular reservoir has already been expelled, and the remaining gas is turbulent and warm, suggesting an ongoing phase of AGN-driven feedback in this post-starburst galaxy. Our results highlight the enormous potential of mid-IR imaging spectroscopy to uncover jet-driven feedback in low-luminosity AGN. Without the spatially resolved MIRI diagnostics, the kinetic power of the AGN in ESO 420-G13 and its role in shaping the host galaxy ISM would have remained hidden.

astro-ph.GA↗

arXiv2026

Cosmic Ray Ionization of Low-Excitation Lines in Active Galactic Nuclei and Starburst Galaxies

Cosmic rays (CRs) can significantly impact dense molecular clouds in galaxies, heating the interstellar medium (ISM) and altering its chemistry, ionization, and thermal properties. Their influence is particularly relevant in environments with high CR rates, such as starburst galaxies with supernova remnants or jets and outflows in active galactic nuclei (AGN). CRs transfer energy to the ionized phase of the ISM far from the ionization source, preventing gas cooling and driving large-scale winds. In this work, we use CLOUDY to explore the effect of CRs on nebular gas, a relatively underexplored area, mainly focused on cold molecular gas. Our models cover a broad range of density ($1 - 10^4\,\rm{cm^{-3}}$), ionization parameter ($-3.5 \leq \log U \leq -1.5$), and CR ionization rate ($10^{-16}\, \rm{s^{-1}} - 10^{-12}\, \rm{s^{-1}}$). These are compared to MUSE observations of two AGN, Centaurus A and NGC 1068, and the starburst NGC 253. We find that CR rates $\gtrsim 10^{-13}\, \rm{s^{-1}}$, typical of AGN and strong starburst galaxies, can significantly alter the thermal structure of the ionized gas by forming a deep secondary low-ionization layer beyond the photoionization-dominated region. This enhances emission from low-ionization transitions, such as [\ion{N}{ii}], [\ion{S}{ii}], and [\ion{O}{i}], affecting line-ratio diagnostics, metallicity, and ionization estimates. Unlike pure photoionization models, AGN simulations with high CR ionization rates reproduce the Seyfert loci in BPT diagrams without requiring super-solar metallicities for the narrow-line region. Additionally, star formation simulations with high CR ionization rates can explain line ratios in the LINER domain. We propose new maximum starburst boundaries for BPT diagrams to distinguish regions dominated by AGN photoionization from those that could be explained by star formation plus high CR ionization rates.

astro-ph.GA↗

arXiv2026

Cosmic-ray impact on optical and mid-infrared emission line diagnostics in NGC 5728

Cosmic rays (CRs), from active galactic nuclei (AGN) jets and supernovae (SNe), serve as a significant feedback mechanism influencing emission lines in narrow line region (NLR) clouds. These highly energetic particles, propelled by shocks, heat the interstellar medium (ISM) and modify its chemical composition. This study investigates the role of CRs, particularly in their ability to excite gas and align with observed line ratios across UV and optical diagnostics. We employ CLOUDY to explore CR ionization rate, ionization parameter, and initial hydrogen density effects on optical and mid-infrared (MIR) emission. Our analysis includes high-quality optical data from the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT) for NGC 5728, supplemented by infrared observations from the James Webb Space Telescope (JWST). Our previous results indicate that CRs are instrumental in heating the inner regions of gas clouds, enhancing emission of low-ionization optical lines. Mid-infrared data reveal that emission lines like [Ar II] and [Ne II] within the JWST Mid-Infrared Instrument (MIRI) field of view are sensitive to CRs. In contrast, high-ionization lines (for example, [Ne V]) serve as robust tracers of photoionization insensitive to CRs. Moreover, mixed optical and MIR diagnostics offer insight into the relative roles of CRs and shocks, which often produce similar signatures in emission lines. We find that while both mechanisms can elevate certain line ratios, their influence on MIR diagnostics diverges: shocks and CRs affect low-ionization lines differently, allowing for a better understanding when multi-wavelength data are available. Our approach not only helps to resolve the degeneracy between metallicity and CR ionization but also enables the potential differentiation of shocks and CR-driven processes in AGN.

astro-ph.GA↗

arXiv2025

High resolution ALMA observations of H$_2$S in LIRGS (Dense gas and shocks in outflows and CNDs)

Molecular gas plays a critical role in regulating star formation and nuclear activity in galaxies. Sulphur bearing molecules, such as H2S, are sensitive to the physical and chemical environments in which they reside and are potential tracers of shocked, dense gas in galactic outflows and active galactic nuclei (AGN). We aim to investigate the origin of H2S emission and its relation to dense gas and outflow activity in the central regions of nearby infrared luminous galaxies. We present ALMA Band 5 observations of the ortho H2S 1(1,0) 1(0,1) transition in three nearby galaxies: NGC 1377, NGC 4418, and NGC 1266. We perform radiative transfer modelling using RADEX to constrain the physical conditions of the H2S emitting gas and compare the results to ancillary CO and continuum data. We detect compact H2S emission in all three galaxies, arising from regions smaller than approximately 150 parsecs. The H2S spectral profiles exhibit broad line wings, suggesting an association with outflowing or shocked gas. In NGC 4418, H2S also appears to be tracing gas that is counterrotating. A peculiar red shifted emission feature may correspond to inflowing gas, or possibly a slanted outflow. RADEX modelling indicates that the H2S emitting gas has high densities (molecular hydrogen density greater than 10^7 cm^-3) and moderately warm temperatures (between 40 and 200 Kelvin). The derived densities exceed those inferred from CO observations, implying that H2S traces denser regions of the interstellar medium.

astro-ph.GA↗

arXiv2024

A case study of gas impacted by black-hole jets with the JWST: outflows, bow shocks, and high excitation of the gas in the galaxy IC5063

We present James Webb Space Telescope MIRI data of the inner 3x2kpc^2 of the galaxy IC5063, in which the jets of a supermassive black hole interact with the gaseous disk they are crossing. Jet-driven outflows were known to be initiated along or near the jet path and to modify the stability of molecular clouds, possibly altering their star formation properties. The MIRI data, of unprecedented resolution and sensitivity in the infrared, now reveal that there are more than ten discrete regions with outflows, nearly doubling the number of such known regions. Outflows exist near the radio lobes, at the nucleus, in a biconical structure perpendicular to the jet, and in a bubble moving against the disk. In some of them, velocities above escape velocity are observed. Stratification is also observed, with higher ionization or excitation gas attaining higher velocities. More outflows and bow shocks, found further away from the nucleus than the radio lobes, in regions without significant radio emission, reveal the existence of past or weak radio jets that interacted with the interstellar medium. The coincidence of the bow shocks with the optical extended emission line region (EELR) suggests that the jets also contributed to the gas ionization. Maps of the H2 gas excitation temperature, T_ex, indicate that the molecular gas is most excited in regions with radio emission. There, T_ex is >100 K higher than in the EELR interior. We argue that a combination of jet-related shocks and cosmic rays is likely responsible for this excess molecular gas excitation.

astro-ph.GA↗

arXiv2022

CO in the ALMA Radio-Source Catalogue (ARC): the molecular gas content of radio galaxies as a function of redshift

To evaluate the role of radio activity in galaxy evolution, we designed a large archival CO survey of radio galaxies (RGs) to determine their molecular gas masses at different epochs. We used a sample of 120 RGs representative of the NVSS 1.4 GHz survey, when flux limited at 0.4 Jy. Of those, 66 galaxies belonged to the ALMA Radio-source Catalogue (ARC) of calibrators and had spectral window tunings around CO (1-0), (2-1), (3-2), or (4-3). We reduced their ALMA data, determined their H2 mass contents, and combined the results with similar results for the remaining 54 galaxies from the literature. We found that, while at all epochs the majority of RGs have undetectable reservoirs, there is a rapid increase in the H2 mass content of the CO-detected RGs with z. At 1<z<2.5, one-fourth of the RGs have at least as much molecular gas as simulations would indicate for a typical halo mass of that epoch. These galaxies plausibly have ``normal'' or even starburst hosts. Taking into account the completeness correction of the sample, we created the corresponding H$_2$ mass functions at 0.005<z<0.3 and 1<z<2.5. The local mass function reveals that the number density of low-z RGs with detectable molecular gas reservoirs is only a little lower (a factor of ~4) than that of pure (or little star-forming) type 1 and 2 AGN in simulations. At 1<z<2.5, there is a significant decrease in the number density of high-z RGs due to the rarity of bright radio galaxies. An estimate for the missing faint RGs would, nonetheless, bring populations close again. Finally, we find that the volume density of molecular gas locked up in the brightest 1/5000-1/7000 RGs is similar in the examined $z$ bins. This result likely indicates that the inflow rate on one hand and the star-formation depletion rate plus the jet-driven expulsion rate on the other hand counteract each other in the most luminous RGs of each epoch.

astro-ph.GA↗

arXiv2022

Linking pressure gradients with the stability of molecular clouds in galactic outflows

The jets launched by actively accreting black holes are capable of launching several of the massive (million or billion solar mass) molecular outflows observed in galaxies. These outflows could suppress or enhance star formation in galaxies. To investigate the stability of clouds capable to form stars in outflows, we modeled CO and HCO+ ALMA data of the galaxy IC5063, in which black-hole jets impact molecular clouds. Using a radiative transfer code that self-consistently performs astrochemical and thermal balance calculations based on the available gas heating sources, we found that mechanical heating and cosmic ray (CR) heating are fully capable of individually reproducing the data. In our best-fit model, CRs provide about 1/3rd of the dense gas heating at the radio lobes, emphasizing the role of this often neglected mechanism in heating the gas and potentially generating outflows. The gas temperature and density indicate that the jet passage leads to an increase of about 1 order of magnitude in the internal pressure Pi of molecular clouds (with Pi/k from 8*10^5 up to 7*10^6 K cm^-3), irrespective of the excitation mechanism. From the fluxes of [S II] and [N II] lines in VLT MUSE data, the external pressure Pe of molecular clouds increases in several regions enough to exceed Pi. This result leads us to conclude that we are observing the expansion of an ionized overpressurized cocoon that compresses molecular clouds and that could lead to their collapse. Some jet-impacted clouds, nonetheless, near pathways that the jet cleared have increased Pi and decreased Pe. They are likely to undergo evaporation of their outer layers. Part of the evaporated layers could mass load the outflow thanks to ram pressure from co-spatial ionized gas flows. The observed pressure changes thus suggest that both star formation enhancement and suppression could simultaneously occur.

astro-ph.GA↗

arXiv2021

Simulating infrared spectro-photometric surveys with a SPRITZ

Mid- and far-infrared (IR) photometric and spectroscopic observations are fundamental to a full understanding of the dust-obscured Universe and the evolution of both star formation and black hole accretion in galaxies. In this work, using the specifications of the SPace Infrared telescope for Cosmology and Astrophysics (SPICA) as a baseline, we investigate the capability to study the dust-obscured Universe of mid- and far-IR photometry at 34 and 70 $μ$m and low-resolution spectroscopy at 17-36 $μ$m using the state-of-the-art Spectro-Photometric Realisations of Infrared-selected Targets at all-z (SPRITZ) simulation. This investigation is also compared to the expected performance of the Origins Space Telescope and the Galaxy Evolution Probe. The photometric view of the Universe of a SPICA-like mission could cover not only bright objects (e.g. L$_{IR}$>10$^{12}$L$_\odot$) up to z=10, but also normal galaxies(L$_{IR}$<10$^{11}$L$_\odot$) up to z$\sim$4. At the same time, the spectroscopic observations of such mission could also allow us to estimate the redshifts and study the physical properties for thousands of star-forming galaxies and active galactic nuclei by observing the polycyclic aromatic hydrocarbons and a large set of IR nebular emission lines. In this way, a cold, 2.5-m size space telescope with spectro-photometric capability analogous to SPICA, could provide us with a complete three-dimensional (i.e. images and integrated spectra) view of the dust-obscured Universe and the physics governing galaxy evolution up to z$\sim$4.

astro-ph.GA↗

arXiv2019

A CO molecular gas wind 340 pc away from the Seyfert 2 nucleus in ESO 420-G13 probes an elusive radio jet

A prominent jet-driven outflow of CO(2-1) molecular gas is found along the kinematic minor axis of the Seyfert 2 galaxy ESO 420-G13, at a distance of $340-600\, \rm{pc}$ from the nucleus. The wind morphology resembles a characteristic funnel shape, formed by a highly collimated filamentary emission at the base, likely tracing the jet propagation through a tenuous medium, until a bifurcation point at $440\, \rm{pc}$ where the jet hits a dense molecular core and shatters, dispersing the molecular gas into several clumps and filaments within the expansion cone. We also trace the jet in ionised gas within the inner $\lesssim 340\, \rm{pc}$ using the [NeII]$_{\rm 12.8 μm}$ line emission, where the molecular gas follows a circular rotation pattern. The wind outflow carries a mass of $\sim 8 \times 10^6\, \rm{M_\odot}$ at an average wind projected speed of $\sim 160\, \rm{km\,s^{-1}}$, which implies a mass outflow rate of $\sim 14\, \rm{M_\odot\,yr^{-1}}$. Based on the structure of the outflow and the budget of energy and momentum, we discard radiation pressure from the active nucleus, star formation, and supernovae as possible launching mechanisms. ESO 420-G13 is the second case after NGC 1377 where the presence of a previously unknown jet is revealed due to its interaction with the interstellar medium, suggesting that unknown jets in feeble radio nuclei might be more common than expected. Two possible jet-cloud configurations are discussed to explain the presence of an outflow at such distance from the AGN. The outflowing gas will likely not escape, thus a delay in the star formation rather than quenching is expected from this interaction, while the feedback effect would be confined within the central few hundred parsecs of the galaxy.

astro-ph.GA↗

arXiv2019

Complex molecular gas kinematics in the inner 5 kpc of 4C12.50 as seen by ALMA

The nearby system 4C12.50, also known as IRAS 13451+1217 and PKS 1345+12, is a merger of gas-rich galaxies with infrared and radio activity. It has a perturbed interstellar medium (ISM) and a dense configuration of gas and dust around the nucleus. The radio emission at small ($\sim$100 pc) and large ($\sim$100 kpc) scales, as well as the large X-ray cavity in which the system is embedded, are indicative of a jet that could have affected the ISM. We carried out observations of the CO(1-0), (3-2), and (4-3) lines with the Atacama Large Millimeter Array (ALMA) to determine basic properties (i.e., extent, mass, and excitation) of the cold molecular gas in this system, including its already-known wind. The CO emission reveals the presence of gaseous streams related to the merger, which result in a small ($\sim$4kpc-wide) disk around the western nucleus. The disk reaches a rotational velocity of 200 $kms^{-1}$ , and has a mass of 3.8($\pm$0.4)$\times$10${^9}M_{\odot}$. It is truncated at a gaseous ridge north of the nucleus that is bright in [O III]. Regions with high-velocity CO emission are seen at signal-to-noise ratios of between 3 and 5 along filaments that radially extend from the nucleus to the ridge and that are bright in [O III] and stellar emission. A tentative wind detection is also reported in the nucleus and in the disk. The molecular gas speed could be as high as 2200 $kms^{-1}$ and the total wind mass could be as high as 1.5($\pm$0.1)$\times$10$^9M_{\odot}$. Energetically, it is possible that the jet, assisted by the radiation pressure of the active nucleus or the stars, accelerated clouds inside an expanding bubble.

astro-ph.GA↗

arXiv2016

ALMA reveals optically thin, highly excited CO gas in the jet-driven winds of the galaxy IC5063

Using CO (4-3) and (2-1) Atacama Large Millimeter Array (ALMA) data, we prove that the molecular gas in the jet-driven winds of the galaxy IC5063 is more highly excited than the rest of the molecular gas in the disk of the same galaxy. On average, the CO(4-3)/CO(2-1) flux ratio is 1 for the disk and 5 for the jet accelerated or impacted gas. Spatially-resolved maps reveal that in regions associated with winds, the CO(4-3)/CO(2-1) flux ratio significantly exceeds the upper limit of 4 for optically thick gas. It frequently takes values between 5 and 11, and it occasionally further approaches the upper limit of 16 for optically thin gas. Excitation temperatures of 30-100 K are common for the molecules in these regions. If all of the outflowing molecular gas is optically thin, at 30-50 K, then its mass is 2*10^6 M_sun. This lower mass limit is an order of magnitude below the mass derived from the CO(2-1) flux in the case of optically thick gas. Molecular winds can thus be less massive, but more easily detectable at high z than they were previously thought to be.

astro-ph.GA↗

arXiv2016

Far-infrared line spectra of active galaxies from the Herschel/PACS Spectrometer: the complete database

We present a coherent database of spectroscopic observations of far-IR fine-structure lines from the Herschel/PACS archive for a sample of 170 local AGN, plus a comparison sample of 20 starburst galaxies and 43 dwarf galaxies. Published Spitzer/IRS and Herschel/SPIRE line fluxes are included to extend our database to the full 10-600 $μm$ spectral range. The observations are compared to a set of CLOUDY photoionisation models to estimate the above physical quantities through different diagnostic diagrams. We confirm the presence of a stratification of gas density in the emission regions of the galaxies, which increases with the ionisation potential of the emission lines. The new [OIV]25.9$μm$/[OIII]88$μm$ vs [NeIII]15.6$μm$/[NeII]12.8$μm$ diagram is proposed as the best diagnostic to separate: $i)$ AGN activity from any kind of star formation; and $ii)$ low-metallicity dwarf galaxies from starburst galaxies. Current stellar atmosphere models fail to reproduce the observed [OIV]25.9$μm$/[OIII]88$μm$ ratios, which are much higher when compared to the predicted values. Finally, the ([NeIII]15.6$μm$ + [NeII]12.8$μm$)/([SIV]10.5$μm$ + [SIII]18.7$μm$) ratio is proposed as a promising metallicity tracer to be used in obscured objects, where optical lines fail to accurately measure the metallicity. The diagnostic power of mid- to far-infrared spectroscopy shown here for local galaxies will be of crucial importance to study galaxy evolution during the dust-obscured phase at the peak of the star formation and black-hole accretion activity ($1 < z < 4$). This study will be addressed by future deep spectroscopic surveys with present and forthcoming facilities such as JWST, ALMA, and SPICA.

astro-ph.GA↗

arXiv2015

A radio jet drives a molecular and atomic gas outflow in multiple regions within one square kiloparsec of the nucleus of the nearby galaxy IC5063

We analyzed near-infrared data of the nearby galaxy IC5063 taken with the Very Large Telescope SINFONI instrument. IC5063 is an elliptical galaxy that has a radio jet nearly aligned with the major axis of a gas disk in its center. The data reveal multiple signatures of molecular and atomic gas that has been kinematically distorted by the passage of the jet plasma or cocoon within an area of ~1 kpc^2. Concrete evidence that the interaction of the jet with the gas causes the gas to accelerate comes from the detection of outflows in four different regions along the jet trail: near the two radio lobes, between the radio emission tip and the optical narrow-line-region cone, and at a region with diffuse 17.8 GHz emission midway between the nucleus and the north radio lobe. The outflow in the latter region is biconical, centered 240 pc away from the nucleus, and oriented perpendicularly to the jet trail. The diffuse emission that is observed as a result of the gas entrainment or scattering unfolds around the trail and away from the nucleus with increasing velocity. It overall extends for >700 pc parallel and perpendicular to the trail. Near the outflow starting points, the gas has a velocity excess of 600 km/s to 1200 km/s with respect to ordered motions, as seen in [FeII], Pa alpha, or H2 lines. High H2 (1-0) S(3)/S(1) flux ratios indicate non-thermal excitation of gas in the diffuse outflow.

astro-ph.GA↗

arXiv2014

Heating of the molecular gas in the massive outflow of the local ultraluminous-infrared and radio-loud galaxy 4C12.50

We present a comparison of the molecular gas properties in the outflow vs. in the ambient medium of the local prototype radio-loud and ultraluminous-infrared galaxy 4C12.50 (IRAS13451+1232), using new data from the IRAM Plateau de Bure interferometer and 30m telescope, and the Herschel space telescope. Previous H_2 (0-0) S(1) and S(2) observations with the Spitzer space telescope had indicated that the warm (~400K) molecular gas in 4C12.50 is made up of a 1.4(+-0.2)x10^8 M_sun ambient reservoir and a 5.2(+-1.7)x10^7 M_sun outflow. The new CO(1-0) data cube indicates that the corresponding cold (25K) H_2 gas mass is 1.0(+-0.1)x10^10 M_sun for the ambient medium and <1.3x10^8 M_sun for the outflow, when using a CO-intensity-to-H_2-mass conversion factor alpha of 0.8 M_sun /(K km/s pc^2). The combined mass outflow rate is high, 230-800 M_sun/yr, but the amount of gas that could escape the galaxy is low. A potential inflow of gas from a 3.3(+-0.3)x10^8 M_sun tidal tail could moderate any mass loss. The mass ratio of warm-to-cold molecular gas is >= 30 times higher in the outflow than in the ambient medium, indicating that a non-negligible fraction of the accelerated gas is heated to temperatures at which star formation is inefficient. This conclusion is robust against the use of different alpha factor values, and/or different warm gas tracers (H_2 vs. H_2 plus CO): with the CO-probed gas mass being at least 40 times lower at 400K than at 25K, the total warm-to-cold mass ratio is always lower in the ambient gas than in the entrained gas. Heating of the molecular gas could facilitate the detection of new outflows in distant galaxies by enhancing their emission in intermediate rotational number CO lines.

astro-ph.GA↗

arXiv2013

Stellar Velocity Dispersion Measurements in High-Luminosity Quasar Hosts and Implications for the AGN Black Hole Mass Scale

We present new stellar velocity dispersion measurements for four luminous quasars with the NIFS instrument and the ALTAIR laser guide star adaptive optics system on the Gemini North 8-m telescope. Stellar velocity dispersion measurements and measurements of the supermassive black hole masses in luminous quasars are necessary to investigate the coevolution of black holes and galaxies, trace the details of accretion, and probe the nature of feedback. We find that higher-luminosity quasars with higher-mass black holes are not offset with respect to the MBH-sigma relation exhibited by lower-luminosity AGNs with lower-mass black holes, nor do we see correlations with galaxy morphology. As part of this analysis, we have recalculated the virial products for the entire sample of reverberation-mapped AGNs and used these data to redetermine the mean virial factor hfi that places the reverberation data on the quiescent M_BH-sigma relation. With our updated measurements and new additions to the AGN sample, we obtain = 4.31 +/- 1.05, which is slightly lower than, but consistent with, most previous determinations.

astro-ph.CO↗

arXiv2012

Evidence for CO shock excitation in NGC 6240 from Herschel SPIRE spectroscopy

We present Herschel SPIRE FTS spectroscopy of the nearby luminous infrared galaxy NGC 6240. In total 20 lines are detected, including CO J=4-3 through J=13-12, 6 H2O rotational lines, and [CI] and [NII] fine-structure lines. The CO to continuum luminosity ratio is 10 times higher in NGC 6240 than Mrk 231. Although the CO ladders of NGC 6240 and Mrk 231 are very similar, UV and/or X-ray irradiation are unlikely to be responsible for the excitation of the gas in NGC 6240. We applied both C and J shock models to the H2 v=1-0 S(1) and v=2-1 S(1) lines and the CO rotational ladder. The CO ladder is best reproduced by a model with shock velocity v_s=10 km s^-1 and a pre-shock density n_H=5 * 10^4 cm^-3. We find that the solution best fitting the H2 lines is degenerate: The shock velocities and number densities range between v_s = 17 - 47 km s^-1 and n_H=10^7 - 5 * 10^4 cm^-3, respectively. The H2 lines thus need a much more powerful shock than the CO lines. We deduce that most of the gas is currently moderately stirred up by slow (10 km s^-1) shocks while only a small fraction (< 1 percent) of the ISM is exposed to the high velocity shocks. This implies that the gas is rapidly loosing its highly turbulent motions. We argue that a high CO line-to-continuum ratio is a key diagnostic for the presence of shocks.

astro-ph.CO↗

arXiv2012

Survival of molecular gas in Virgo's hot intracluster medium: CO near M86

We carried out CO(1-0) and CO(2-1) observations of 21 different regions in the vicinity of M86, NGC4438, and along the 120 kpc-long, Ha-emitting filamentary trail that connects them, aiming to test whether molecular gas can survive to be transferred from a spiral to an elliptical galaxy in Virgo's 10^7K intracluster medium (ICM). We targeted Ha-emitting regions that could be associated with the interface between cold molecular clouds and the hot ionized ICM. The data, obtained with the 30m telescope of the Institut de Radioastronomie Millimetrique, led to the detection of molecular gas close to M86. CO gas with a recession velocity that is similar to that of the stars, -265 km/s, and with a corresponding H2 mass of 2*10^7 M_sun, was detected ~10 kpc southeast of the nucleus of M86, near the peak of its HI emission. We argue that it is possible for this molecular gas either to have formed in situ from HI, or to have been stripped from NGC4438 directly in molecular form. In situ formation is nonetheless negligible for the 7*10^6 M_sun of gas detected at 12:26:15.9+12:58:49, at ~10 kpc northeast of M86, where no (strong) HI emission is present. This detection provides evidence for the survival of molecular gas in filaments for timescales of ~100 Myr. An amount equivalent to 5*10^7 M_sun of H2 gas that could be lost to the ICM or to neighboring galaxies was also discovered in the tidal tail northwest of NGC4438. A scenario of gas being alternatively brought to M86 from NGC4388 on its south was also examined but it was considered unlikely due to the non detection of CO below or at the HI stream velocities, 2000-2700 km/s.

astro-ph.CO↗

arXiv2012

Cold and warm molecular gas in the outflow of 4C12.50

We present deep observations of the 12CO(1-0) and (3-2) lines in the ultra-luminous infrared and radio galaxy 4C12.50, carried out with the 30m telescope of the Institut de Radioastronomie Millimetrique. Our observations reveal the cold molecular gas component of a warm molecular gas outflow that was previously known from Spitzer Space Telescope data. The 12CO(3-2) profile indicates the presence of absorption at -950 km/s from systemic velocity with a central optical depth of 0.22. Its profile is similar to that of the HI absorption that was seen in radio data of this source. A potential detection of the (0-1) absorption enabled us to place an upper limit of 0.03 on its central optical depth, and to constrain the excitation temperature of the outflowing CO gas to >=65K assuming that the gas is thermalized. If the molecular clouds fully obscure the background millimeter continuum that is emitted by the radio core, the H2 column density is >=1.8*10^22 /cm^2. The outflow then carries an estimated cold H2 mass of at least 4.2*10^3 M_sun along the nuclear line of sight. This mass will be even higher when integrated over several lines of sight, but if it were to exceed 3*10^9 M_sun, the outflow would most likely be seen in emission. Since the ambient cold gas reservoir of 4C12.50 is 1.0*10^10 M_sun, the outflowing-to-ambient mass ratio of the warm gas (37%) could be elevated with respect to that of the cold gas.

astro-ph.CO↗