arXiv subjects

S. Aalto

Publications and source records attributed to S. Aalto.

At least 55 records · Page 3Linked to original sources

arXiv2021

Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde IV. The ALMA view of N113 and N159W in the LMC

We mapped the kinetic temperature structure of two massive star-forming regions, N113 and N159W, in the Large Magellanic Cloud (LMC). We have used $\sim$1\hbox{$\,.\!\!^{\prime\prime}$}6\,($\sim$0.4\,pc) resolution measurements of the para-H$_2$CO\,$J_{\rm K_ aK_c}$\,=\,3$_{03}$--2$_{02}$, 3$_{22}$--2$_{21}$, and 3$_{21}$--2$_{20}$ transitions near 218.5\,GHz to constrain RADEX non-LTE models of the physical conditions. The gas kinetic temperatures derived from the para-H$_2$CO line ratios 3$_{22}$--2$_{21}$/3$_{03}$--2$_{02}$ and 3$_{21}$--2$_{20}$/3$_{03}$--2$_{02}$ range from 28 to 105\,K in N113 and 29 to 68\,K in N159W. Distributions of the dense gas traced by para-H$_2$CO agree with those of the 1.3\,mm dust and \emph{Spitzer}\,8.0\,$μ$m emission, but do not significantly correlate with the H$α$ emission. The high kinetic temperatures ($T_{\rm kin}$\,$\gtrsim$\,50\,K) of the dense gas traced by para-H$_2$CO appear to be correlated with the embedded infrared sources inside the clouds and/or YSOs in the N113 and N159W regions. The lower temperatures ($T_{\rm kin}$\,$<$\,50\,K) are measured at the outskirts of the H$_2$CO-bearing distributions of both N113 and N159W. It seems that the kinetic temperatures of the dense gas traced by para-H$_2$CO are weakly affected by the external sources of the H$α$ emission. The non-thermal velocity dispersions of para-H$_2$CO are well correlated with the gas kinetic temperatures in the N113 region, implying that the higher kinetic temperature traced by para-H$_2$CO is related to turbulence on a $\sim$0.4\,pc scale. The dense gas heating appears to be dominated by internal star formation activity, radiation, and/or turbulence. It seems that the mechanism heating the dense gas of the star-forming regions in the LMC is consistent with that in Galactic massive star-forming regions located in the Galactic plane.

astro-ph.GA↗

arXiv2021

A hard X-ray view of Luminous and Ultra-luminous Infrared Galaxies in GOALS: I - AGN obscuration along the merger sequence

The merger of two or more galaxies can enhance the inflow of material from galactic scales into the close environments of Active Galactic Nuclei (AGN), obscuring and feeding the supermassive black hole (SMBH). Both recent simulations and observations of AGN in mergers have confirmed that mergers are related to strong nuclear obscuration. However, it is still unclear how AGN obscuration evolves in the last phases of the merger process. We study a sample of 60 Luminous and Ultra-luminous IR galaxies (U/LIRGs) from the GOALS sample observed by NuSTAR. We find that the fraction of AGN that are Compton-thick (CT; $N_{\rm H}\geq 10^{24}\rm\,cm^{-2}$) peaks at $74_{-19}^{+14}\%$ at a late merger stage, prior to coalescence, when the nuclei have projected separations of $d_{\rm sep}\sim 0.4-6$ kpc. A similar peak is also observed in the median $N_{\rm H}$ [$(1.6\pm0.5)\times10^{24}\rm\,cm^{-2}$]. The vast majority ($85^{+7}_{-9}\%$) of the AGN in the final merger stages ($d_{\rm sep}\lesssim 10$ kpc) are heavily obscured ($N_{\rm H}\geq 10^{23}\rm\,cm^{-2}$), and the median $N_{\rm H}$ of the accreting SMBHs in our sample is systematically higher than that of local hard X-ray selected AGN, regardless of the merger stage. This implies that these objects have very obscured nuclear environments, with the $N_{\rm H}\geq 10^{23}\rm\,cm^{-2}$ gas almost completely covering the AGN in late mergers. CT AGN tend to have systematically higher absorption-corrected X-ray luminosities than less obscured sources. This could either be due to an evolutionary effect, with more obscured sources accreting more rapidly because they have more gas available in their surroundings, or to a selection bias. The latter scenario would imply that we are still missing a large fraction of heavily obscured, lower luminosity ($L_{2-10}\lesssim 10^{43}\rm\,erg\,s^{-1}$) AGN in U/LIRGs.

astro-ph.GA↗

arXiv2021

Molecular gas kinematics in the nuclear region of nearby Seyfert galaxies with ALMA

We present the analysis of the molecular gas in the nuclear regions of NGC 4968, NGC 4845, and MCG-06-30-15, with the help of ALMA observations of the CO(2-1) emission line. The aim is to determine the kinematics of the gas in the central (~ 1 kpc) region. We use the 3D-Based Analysis of Rotating Object via Line Observations ($^{3D}$BAROLO) and DiskFit softwares. Circular motions dominate the kinematics of the gas in the central discs, mainly in NGC 4845 and MCG-06-30-15, however there is a clear evidence of non-circular motions in the central ($\sim$ 1 kpc) region of NGC 4845 and NGC 4968. The strongest non-circular motion is detected in the inner disc of NGC 4968 with velocity $\sim 115\, \rm{km\,s^{-1}}$. The bisymmetric model is found to give the best-fit for NGC 4968 and NGC 4845. If the dynamics of NGC 4968 is modeled as a corotation pattern just outside of the bar, the bar pattern speed turns out to be at $Ω_b$ = $52\, \rm{km\,s^{-1}\,kpc^{-1}}$ the corotation is set at 3.5 kpc and the inner Lindblad resonance (ILR) ring at R = 300pc corresponding to the CO emission ring. The 1.2 mm ALMA continuum is peaked and compact in NGC 4968 and MCG-06-30-15, but their CO(2-1) has an extended distribution. Allowing the CO-to-H$_{2}$ conversion factor $α_{CO}$ between 0.8 and 3.2, typical of nearby galaxies of the same type, the molecular mass M(H$_{2}$) is estimated to be $\sim 3-12\times 10^{7} ~{\rm M_\odot}$ (NGC 4968), $\sim 9-36\times 10^{7}~ {\rm M_\odot}$ (NGC 4845), and $\sim 1-4\times 10^{7}~ {\rm M_\odot}$ (MCG-06-30-15). We conclude that the observed non-circular motions in the disc of NGC 4968 and likely that seen in NGC 4845 is due to the presence of the bar in the nuclear region. At the current spectral and spatial resolution and sensitivity we cannot claim any strong evidence in these sources of the long sought feedback/feeding effect due to the AGN presence.

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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 Giant Molecular Cloud Catalog in the Molecular Disk of the Elliptical Galaxy NGC 5128 (Centaurus A)

We present the first census of giant molecular clouds (GMCs) complete down to 10$^6 M_{\odot}$ and within the inner 4 kpc of the nearest giant elliptical and powerful radio galaxy, Centaurus A. We identified 689 GMCs using CO(1--0) data with 1" spatial resolution ($\sim 20$ pc) and 2 km/s velocity resolution obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). The $I$(CO)-$N$(H$_2$) conversion factor based on the virial method is $X_{\rm CO}$ = $(2 \pm 1 )\times10^{20}$ cm$^{-2}$(K km/s)$^{-1}$ for the entire molecular disk, consistent with that of the disks of spiral galaxies including the Milky Way, and $X_{\rm CO}$ = $(5 \pm 2)\times10^{20}$ cm$^{-2}$(K km/s)$^{-1}$ for the circumnuclear disk (CND, within a galactocentric radius of 200 pc). We obtained the GMC mass spectrum distribution and find that the best-truncated power-law fit for the whole molecular disk, with index $γ\simeq -2.41 \pm 0.02$ and upper cutoff mass $\sim 1.3 \times 10^{7} M_{\odot}$, is also in agreement with that of nearby disk galaxies. A trend is found in the mass spectrum index from steep to shallow as we move to inner radii. Although the GMCs are in an elliptical galaxy, the general GMC properties in the molecular disk are as in spiral galaxies. However, in the CND, large offsets in the line-width-size scaling relations ($\sim$ 0.3 dex higher than those in the GMCs in the molecular disk), a different $X_{\rm CO}$ factor, and the shallowest GMC mass distribution shape ($γ= -1.1 \pm 0.2$) all suggest that there the GMCs are most strongly affected by the presence of the AGN and/or shear motions.

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arXiv2021

Observed CN and HCN intensity ratios exhibit subtle variations in extreme galaxy environments

We use both new and archival ALMA data of three energy lines each of CN and HCN to explore intensity ratios in dense gas in NGC 3256, NGC 7469, and IRAS 13120-5453. The HCN (3-2)/HCN (1-0) intensity ratio varies in NGC 3256 and NGC 7469, with superlinear trends of 1.53$\pm$0.07 and 1.55$\pm$0.05, respectively. We find an offset to higher HCN (3-2)/HCN (1-0) intensity ratios (~0.8) in IRAS 13120-5453 compared to NGC 3256 (~0.3-0.4) and NGC 7469 (~0.3-0.5). The HCN (4-3)/HCN (3-2) intensity ratio in NGC 7469 has a slope of 1.34$\pm$0.05. We attribute the variation within NGC 3256 to excitation associated with the northern and southern nuclei. In NGC 7469, the variations are localized to the region surrounding the active galactic nucleus. At our resolution (~700 pc), IRAS 13120-5453 shows little variation in the HCN intensity ratios. Individual galaxies show nearly constant CN (2-1)/CN (1-0) intensity ratios. We find an offset to lower CN (2-1)/CN (1-0) intensity ratios (~0.5) in NGC 3256 compared to the other two galaxies (~0.8). For the CN (3-2)/CN (2-1) intensity ratio, NGC 7469 has a superlinear trend of 1.55$\pm$0.04, with the peak localized toward the active galactic nucleus. We find high (~1.7) CN (1-0)/HCN (1-0) intensity ratios in IRAS 13120-5453 and in the northern nucleus of NGC 3256, compared to a more constant ratio (~1.1) in NGC 7469 and non-starbursting regions of NGC 3256.

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arXiv2021

CON-quest: Searching for the most obscured galaxy nuclei

Some luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) host extremely compact and dusty nuclei. The intense infrared radiation arising from warm dust in these sources is prone to excite vibrational levels of molecules such as HCN. This results in emission from the rotational transitions of vibrationally excited HCN (HCN-vib), with the brightest emission found in compact obscured nuclei (CONs). We aim to establish how common CONs are in the local Universe, and whether their prevalence depends on the luminosity or other properties of the host galaxy. We have conducted an Atacama Large Millimeter/submillimeter Array (ALMA) survey of the rotational J=3-2 transition of HCN-vib in a sample of 46 far-infrared luminous galaxies. Compact obscured nuclei are identified in 38 percent of ULIRGs, 21 percent of LIRGs, and 0 percent of lower luminosity galaxies. We find no dependence on the inclination of the host galaxy, but strong evidence of lower IRAS 25 to 60 μm flux density ratios (f25/f60) in CONs compared to the rest of the sample. Furthermore, we find that CONs have stronger silicate features (s9.7μm) but similar PAH equivalent widths (EQW6.2μm) compared to other galaxies. In the local Universe, CONs are primarily found in (U)LIRGs. High resolution continuum observations of the individual nuclei are required to determine if the CON phenomenon is related to the inclinations of the nuclear disks. The lower f25/f60 ratios in CONs as well as the results for the mid-infrared diagnostics investigated are consistent with large dust columns shifting the nuclear radiation to longer wavelengths, making the mid- and far-infrared "photospheres" significantly cooler than the interior regions. To assess the importance of CONs in the context of galaxy evolution, it is necessary to extend this study to higher redshifts where (U)LIRGs are more common.

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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

Detection of H2O and OH+ in z>3 Hot Dust-Obscured Galaxies

In this paper we present the detection of H2O and OH+ emission in z>3 hot dust-obscured galaxies (Hot DOGs). Using ALMA Band-6 observations of two Hot DOGs, we have detected H2O(2_02-1_11) in W0149+2350, and H2O(3_12-3_03) and the multiplet OH+(1_1-0_1) in W0410-0913. We find that both sources have luminous H2O emission with line luminosities of L_H2O > 2.2x10^8 Lsol and L_H2O = 8.7x10^8 Lsol for W0149+2350 and W0410-0913, respectively. The H2O line profiles are similar to those seen for the neighbouring CO(9-8) line, with linewidths of FWHM ~ 800-1000 km/s. However, the H2O emission seems to be more compact than the CO(9-8). OH+ is detected in emission for W0410-0913, with a FWHM=1000km/s and a line luminosity of L_OH+ = 6.92x10^8 Lsol. The ratio of the observed H2O line luminosity over the IR luminosity, for both Hot DOGs, is consistent with previously observed star forming galaxies and AGN. The H2O/CO line ratio of both Hot DOGs and the OH+/H2O line ratio of W0410-0913 are comparable to those of luminous AGN in the literature. The bright H2O(2_02-1_11), and H2O(3_12-3_03) emission lines are likely due to the combined high star formation levels and luminous AGN in these sources. The presence of OH+ in emission, and the agreement of the observed line ratios of the Hot DOGs with luminous AGN in the literature, would suggest that the AGN emission is dominating the radiative output of these galaxies. However, followup multi-transition observations are needed to better constrain the properties of these systems.

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arXiv2020

LeMMINGs. II. The e-MERLIN legacy survey of nearby galaxies. The deepest radio view of the Palomar sample on parsec scale

We present the second data release of high-resolution ($\leq0.2$ arcsec) 1.5-GHz radio images of 177 nearby galaxies from the Palomar sample, observed with the e-MERLIN array, as part of the LeMMINGs (Legacy e-MERLIN Multi-band Imaging of Nearby Galaxy Sample) survey. Together with the 103 targets of the first LeMMINGs data release, this represents a complete sample of 280 local active (LINER and Seyfert) and inactive galaxies HII galaxies and Absorption Line Galaxies, ALG). This large program is the deepest radio survey of the local Universe, $\gtrsim$10$^{17.6}$ W Hz$^{-1}$, regardless of the host and nuclear type: we detect radio emission $\gtrsim$0.25 mJy beam$^{-1}$ for 125/280 galaxies (44.6 per cent) with sizes of typically $\lesssim$100 pc. Of those 125, 106 targets show a core which coincides within 1.2 arcsec with the optical nucleus. Although we observed mostly cores, around one third of the detected galaxies features jetted morphologies. The detected radio core luminosities of the sample range between $\sim$10$^{34}$ and 10$^{40}$ erg s$^{-1}$. LINERs and Seyferts are the most luminous sources, whereas HII galaxies are the least. LINERs show FRI-like core-brightened radio structures, while Seyferts reveal the highest fraction of symmetric morphologies. The majority of HII galaxies have single radio core or complex extended structures, which probably conceal a nuclear starburst and/or a weak active nucleus (seven of them show clear jets). ALGs, which are typically found in evolved ellipticals, although the least numerous, exhibit on average the most luminous radio structures, similar to LINERs.

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arXiv2020

LEGO II: A 3 mm molecular line study covering 100 pc of one of the most actively star-forming portions within the Milky Way Disc

The current generation of (sub)mm-telescopes has allowed molecular line emission to become a major tool for studying the physical, kinematic, and chemical properties of extragalactic systems, yet exploiting these observations requires a detailed understanding of where emission lines originate within the Milky Way. In this paper, we present 60$^{\prime\prime}$ ($\sim$3pc) resolution observations of many 3mm-band molecular lines across a large map of the W49 massive star-forming region ($\sim$100$\times$100pc at 11kpc), which were taken as part of the "LEGO" IRAM-30m large project. We find that the spatial extent or brightness of the molecular line transitions are not well correlated with their critical densities, highlighting abundance and optical depth must be considered when estimating line emission characteristics. We explore how the total emission and emission efficiency (i.e. line brightness per H$_{2}$ column density) of the line emission vary as a function of molecular hydrogen column density and dust temperature. We find that there is not a single region of this parameter space responsible for the brightest and most efficiently emitting gas for all species. For example, we find that the HCN transition shows high emission efficiency at high column density ($10^{22}$cm$^{-2}$) and moderate temperatures (35K), whilst e.g. N$_2$H$^+$ emits most efficiently towards lower temperatures ($10^{22}$cm$^{-2}$; <20K). We determine $X_{\mathrm{CO} (1-0)} \sim 0.3 \times 10^{20} \mathrm{cm^{-2}(Kkms^{-1})^{-1}}$, and $α_{\mathrm{HCN} (1-0)} \sim 30\mathrm{M_\odot(Kkms^{-1}pc^2)^{-1}}$, which both differ significantly from the commonly adopted values. In all, these results suggest caution should be taken when interpreting molecular line emission.

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arXiv2020

Star cluster formation in the most extreme environments: Insights from the HiPEEC survey

We present the Hubble imaging Probe of Extreme Environments and Clusters (HiPEEC) survey. We fit HST NUV to NIR broadband and H$α$ fluxes, to derive star cluster ages, masses, extinctions and determine the star formation rate (SFR) of 6 merging galaxies. These systems are excellent laboratories to trace cluster formation under extreme gas physical conditions, rare in the local universe, but typical for star-forming galaxies at cosmic noon. We detect clusters with ages of 1-500 Myr and masses that exceed $10^7$ M$_\odot$. The recent cluster formation history and their distribution within the host galaxies suggest that systems like NGC34, NGC1614, NGC4194 are close to their final coalescing phase, while NGC3256, NGC3690, NGC6052 are at an earlier/intermediate stage. A Bayesian analysis of the cluster mass function in the age interval 1-100 Myr provides strong evidence in 4 of the 6 galaxies that an exponentially truncated power law better describes the observed mass distributions. For two galaxies, the fits are inconclusive due to low number statistics. We determine power-law slopes $β\sim-1.5$ to $-2.0$, and truncation masses, M$_c$, between $10^6$ and a few times $10^7$ M$_\odot$, among the highest values reported in the literature. Advanced mergers have higher M$_c$ than early/intermediate merger stage galaxies, suggesting rapid changes in the dense gas conditions during the merger. We compare the total stellar mass in clusters to the SFR of the galaxy, finding that these systems are among the most efficient environments to form star clusters in the local universe.

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arXiv2020

ALMA resolves the remarkable molecular jet and rotating wind in the extremely radio-quiet galaxy NGC 1377

Submillimetre and millimetre observations are important in probing the properties of the molecular gas and dust around obscured active galactic nuclei (AGNs) and their feedback. With very high-resolution (0."02x0."03 (2x3 pc)) ALMA 345 GHz observations of CO 3-2, HCO$^+$ 4-3, HCN 4-3 $ν_2$=1$f$, and continuum we have studied the molecular outflow and nucleus of the extremely radio-quiet lenticular galaxy NGC1377. The outflow is resolved, revealing a 150 pc long, clumpy, high-velocity, collimated molecular jet. The molecular emission is emerging from the spine of the jet with an average diameter of 3-7 pc. A narrow-angle, rotating molecular wind surrounds the jet and is enveloped by a larger-scale, slower CO-emitting structure. The jet and narrow wind are turbulent ($σ>$40 kms$^{-1}$) and have steep radial gas excitation gradients. The jet shows velocity reversals that we propose are caused by precession, or episodic directional changes. We suggest that an important process powering the outflow is magneto-centrifugal driving. In contrast, the large-scale CO-envelope may be a slow wind, or cocoon that stems from jet-wind interactions. An asymmetric, nuclear r$\sim$2 pc and hot (>180 K) dust structure with a high molecular column density, N(H$_2$)$\sim1.8 \times 10^{24}$ cm$^{-2}$, is detected in continuum and vibrationally excited HCN. Its luminosity is likely powered by a buried AGN. The mass of the supermassive black hole (SMBH) is estimated to $\sim9\times10^6$ M$_\odot$ and the SMBH of NGC1377 appears to be at the end of an intense phase of accretion. The nuclear growth may be fuelled by low-angular momentum gas inflowing from gas ejected in the molecular jet and wind. Such a feedback-loop of cyclic accretion and outflows would be an effective process in growing the nuclear SMBH. This result invites new questions as to SMBH growth processes in obscured, dusty galaxies.

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arXiv2020

ALMA observations of CS in NGC 1068: chemistry and excitation

We present results from Atacama Large Millimeter/submillimeter Array (ALMA) observations of CS from the nearby galaxy NGC 1068 ($\sim14$ Mpc). This Seyfert 2 barred galaxy possesses a circumnuclear disc (CND, $r\sim200$ pc) and a starburst ring (SB ring, $r\sim1.3$ kpc). These high-resolution maps ($\sim0.5$", $\sim35$ pc) allow us to analyse specific sub-regions in the galaxy and investigate differences in line intensity ratios and physical conditions, particularly those between the CND and SB ring. Local thermodynamic equilibrium (LTE) analysis of the gas is used to calculate CS densities in each sub-region, followed by non-LTE analysis conducted using the radiative transfer code RADEX to fit observations and constrain gas temperature, CS column density and hydrogen density. Finally, the chemical code UCLCHEM is used to reconstruct the gas, allowing an insight into its origin and chemical history. The density of hydrogen in the CND is found to be $\geq10^5$ cm$^{-2}$, although exact values vary, reaching $10^6$ cm$^{-2}$ at the AGN. The conditions in the two arms of the SB ring appear similar to one another, though the density found ($\sim10^4$ cm$^{-2}$) is lower than in the CND. The temperature in the CND increases from east to west, and is also overall greater than found in the SB ring. These modelling methods indicate the requirement for multi-phase gas components in order to fit the observed emission over the galaxy. A larger number of high resolution transitions across the SLED may allow for further constraining of the conditions, particularly in the SB ring.

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arXiv2020

A Hard X-ray Test of HCN Enhancements as a Tracer of Embedded Black Hole Growth

Enhanced emission from the dense gas tracer HCN (relative to HCO$^+ $) has been proposed as a signature of active galactic nuclei (AGN). In a previous single-dish millimeter line survey we identified galaxies with HCN/HCO$ ^+ $ (1-0) intensity ratios consistent with those of many AGN but whose mid-infrared spectral diagnostics are consistent with little to no ( $\lesssim15\% $) contribution of an AGN to the bolometric luminosity. To search for putative heavily obscured AGN, we present and analyze \nustar hard X-ray (3-79 keV) observations of four such galaxies from the Great Observatories All-sky LIRG Survey. We find no X-ray evidence for AGN in three of the systems and place strong upper limits on the energetic contribution of any heavily obscured ($N_{\rm H}>10^{24}$ cm$^{-2}$) AGN to their bolometric luminosity. The X-ray flux upper limits are presently an order of magnitude below what XDR-driven chemistry model predict are necessary to drive HCN enhancements. In a fourth system we find a hard X-ray excess consistent with the presence of an AGN, but contributing only $\sim3\%$ of the bolometric luminosity. It is also unclear if the AGN is spatially associated with the HCN enhancement. We further explore the relationship between HCN/HCO$^+$ (for several $\mathrm{J}_\mathrm{upper}$ levels) and $L_\mathrm{AGN}/L_\mathrm{IR}$ for a larger sample of systems in the literature. We find no evidence for correlations between the line ratios and the AGN fraction derived from X-rays, indicating that HCN/HCO$^+$ intensity ratios are not driven by the energetic dominance of AGN, nor are they reliable indicators of whether SMBH accretion is ongoing.

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arXiv2020

Detection of deuterated molecules, but not of lithium hydride, in the z=0.89 absorber toward PKS1830-211

Deuterium and lithium are light elements of high cosmological and astrophysical importance. In this work we report the first detection of deuterated molecules and a search for lithium hydride, 7LiH, at redshift z=0.89 in the spiral galaxy intercepting the line of sight to the quasar PKS1830-211. We used ALMA to observe several submillimeter lines of ND, NH2D, and HDO, and their related isotopomers NH2, NH3, and H2^18O, in absorption against the southwest image of the quasar, allowing us to derive XD/XH abundance ratios. The absorption spectra mainly consist of two distinct narrow velocity components for which we find remarkable differences. One velocity component shows XD/XH abundances that is about 10 times larger than the primordial elemental D/H ratio, and no variability of the absorption profile during the time span of our observations. [...] The second component has XD/XH abundances that are 100 times larger than the primordial D/H ratio, a deepening of the absorption by a factor of two within a few months, and a rich chemical composition, with relative enhancements of N2H+, CH3OH, SO2, and complex organic molecules. We therefore speculate that this component is associated with the analog of a Galactic dark cloud, while the first component is likely more diffuse. Our search for the 7LiH (1--0) line was unsuccessful and we derive an upper limit 7LiH/H2 = 4 x 10^-13 (3sigma) in the z=0.89 absorber toward PKS1830-211. Besides, with ALMA archival data, we could not confirm the previous tentative detections of this line in the z=0.68 absorber toward B0218+357; we derive an upper limit 7LiH/H2 = 5 x 10^-11 (3sigma), although this is less constraining than our limit toward PKS1830-211. We conclude that, as in the Milky Way, only a tiny fraction of lithium nuclei are possibly bound in LiH in these absorbers at intermediate redshift.

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arXiv2019

Star Formation Efficiencies at Giant Molecular Cloud Scales in the Molecular Disk of the Elliptical Galaxy NGC 5128 (Centaurus A)

We present ALMA CO(1-0) observations toward the dust lane of the nearest elliptical and radio galaxy, NGC 5128 (Centaurus A), with high angular resolution ($\sim$ 1 arcsec, or 18 pc), including information from large to small spatial scales and total flux. We find a total molecular gas mass of 1.6$\times$10$^9$ $M_\odot$ and we reveal the presence of filamentary components more extended than previously seen, up to a radius of 4 kpc. We find that the global star formation rate is $\sim$1 \Msol yr$^{-1}$, which yields a star formation efficiency (SFE) of 0.6 Gyr$^{-1}$ (depletion time $τ=$1.5 Gyr), similar to those in disk galaxies. We show the most detailed view to date (40\,pc resolution) of the relation between molecular gas and star formation within the stellar component of an elliptical galaxy, from several kpc scale to the circumnuclear region close to the powerful radio jet. Although on average the SFEs are similar to those of spiral galaxies, the circumnuclear disk (CND) presents SFEs of 0.3 Gyr$^{-1}$, lower by a factor of 4 than the outer disk. The low SFE in the CND is in contrast to the high SFEs found in the literature for the circumnuclear regions of some nearby disk galaxies with nuclear activity, probably as a result of larger shear motions and longer AGN feedback. The higher SFEs in the outer disk suggests that only central molecular gas or filaments with sufficient density and strong shear motions will remain in $\sim$1 Gyr, which will later result in the compact molecular distributions and low SFEs usually seen in other giant ellipticals with cold gas.

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arXiv2019

Molecular outflows in local galaxies: Method comparison and a role of intermittent AGN driving

We report new detections and limits from a NOEMA and ALMA CO(1-0) search for molecular outflows in 13 local galaxies with high FIR surface brightness, and combine with results from the literature. CO line ratios and outflow structure provide some constraints on the conversion from observables to quantities such as molecular mass outflow rates. Ratios between outflow emission in higher J CO transitions and in CO(1-0) typically are consistent with excitation Ri1<~1. For IRAS 13120-5453, however, R31=2.10 indicates optically thin CO in the outflow. Like much of the outflow literature, we use alpha(CO) = 0.8, and we present arguments for using C=1 in deriving molecular mass outflow rates Mdot = C*M*v/R. We compare the two main methods for molecular outflow detection: CO mm interferometry and Herschel OH spectroscopy. For 26 sources studied with both methods, we find 80% agreement in detecting vout>~150km/s outflows, and non-matches can be plausibly ascribed to outflow geometry and SNR. For 12 bright ULIRGs with detailed OH-based outflow modeling, CO outflows are detected in all but one. Outflow masses, velocities, and sizes for these 11 sources agree well between the two methods, and modest remaining differences may relate to the different but overlapping regions sampled by CO emission and OH absorption. Outflow properties correlate better with AGN luminosity and with bolometric luminosity than with FIR surface brightness. The most massive outflows are found for systems with current AGN activity, but significant outflows in non-AGN systems must relate to star formation or to AGN activity in the recent past. We report scaling relations for the increase of outflow mass, rate, momentum rate, and kinetic power with bolometric luminosity. Short ~10^6yr flow times and some sources with resolved multiple outflow episodes support a role of intermittent driving, likely by AGN. (abridged)

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