Luminosity Ratio Research Articles

Observations of neutral carbon in 29 high-z lensed dusty star-forming galaxies and the comparison of gas mass tracers

Context. The nature and evolution of high-redshift dusty star-forming galaxies (high-z DSFGs) remain open questions. Their massive gas reservoirs play an important role in driving the intense star formation rates hosted in these galaxies. Aims. Our aim is to estimate the molecular gas content of high-z DSFGs by using various gas mass tracers, such as the [CI], CO, [CII] emission lines and the dust content. These tracers need to be well calibrated as they are all limited by uncertainties on factors such as αCO, XCI, α[CII], and δGDR, thereby affecting the accurate determination of the gas mass. The main goal of our work is to check the consistency between the gas mass tracers and to cross-calibrate the uncertain factors. Methods. We observed the two [CI] line transitions for 29 South Pole telescope Submillimeter Galaxies (SPT-SMGs) with the Atacama Large Millimeter/submillimeter Array–Atacama Compact Array (ALMA-ACA). Additionally, we also present new Atacama Pathfinder EXperiment (APEX) observations of [CII] line for nine of these galaxies. We combined our observations with the rich ancillary data of low- and mid-J CO lines, ancillary [CII] line, and dust mass estimations for these galaxies. Results. We find a nearly linear relation between the infrared luminosity and [CI] luminosity if we fit the starbursts and main-sequence galaxies separately. We measure a median [CI]-derived excitation temperature of 34.5 ± 2.1 K. We probed the properties of the interstellar medium (ISM), such as density and radiation field intensity, using [CI] to mid- or high-J CO lines and the [CI]-to-infrared luminosity ratio, and find similar values to the SMG populations in the literature. Finally, the gas masses estimated from [CI], CO, dust, and [CII] do not exhibit any significant trend with the infrared luminosity or the dust temperature. We provide the various cross-calibrations between these tracers. Conclusions. Our study confirms that [CI] is a suitable tracer of the molecular gas content, and shows an overall agreement between all the classical gas tracers used at high redshift. However, their absolute calibration, and thus the gas depletion timescale measurements, remain uncertain.

A Spatially Resolved Analysis of Star Formation Burstiness by Comparing UV and Hα in Galaxies at z ∼ 1 with UVCANDELS

The UltraViolet imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Fields (UVCANDELS) program provides Hubble Space Telescope (HST)/UVIS F275W imaging for four CANDELS fields. We combine this UV imaging with existing HST/near-IR grism spectroscopy from 3D-HST+AGHAST to directly compare the resolved rest-frame UV and Hα emission for a sample of 979 galaxies at 0.7 < z < 1.5, spanning a range in stellar mass of 108−11.5 M ⊙. Using a stacking analysis, we perform a resolved comparison between homogenized maps of rest-UV and Hα to compute the average UV-to-Hα luminosity ratio (an indicator of burstiness in star formation) as a function of galactocentric radius. We find that galaxies below stellar mass of ∼109.5 M ⊙, at all radii, have a UV-to-Hα ratio higher than the equilibrium value expected from constant star formation, indicating a significant contribution from bursty star formation. Even for galaxies with stellar mass ≳109.5 M ⊙, the UV-to-Hα ratio is elevated toward their outskirts (R/R eff > 1.5), suggesting that bursty star formation is likely prevalent in the outskirts of even the most massive galaxies, but is likely overshadowed by their brighter cores. Furthermore, we present the UV-to-Hα ratio as a function of galaxy surface brightness, a proxy for stellar mass surface density, and find that regions below ∼107.5 M ⊙ kpc−2 are consistent with bursty star formation, regardless of their galaxy stellar mass, potentially suggesting that local star formation is independent of global galaxy properties at the smallest scales. Last, we find galaxies at z > 1.1 to have bursty star formation, regardless of radius or surface brightness.

Machine learning and galaxy morphology: for what purpose?

ABSTRACT Classification of galaxies is traditionally associated with their morphologies through visual inspection of images. The amount of data to come render this task, inhuman and Machine Learning (mainly Deep Learning) has been called to the rescue for more than a decade. However, the results look mitigate and there seems to be a shift away from the paradigm of the traditional morphological classification of galaxies. In this paper, I want to show that the algorithms indeed are very sensitive to the features present in images, features that do not necessarily correspond to the Hubble or de Vaucouleurs vision of a galaxy. However, this does not preclude to get the correct insights into the physics of galaxies. I have applied a state-of-the-art ‘traditional’ Machine Learning clustering tool, called Fisher-EM, a latent discriminant subspace Gaussian mixture model algorithm to 4458 galaxies carefully classified into 18 types by the EFIGI project. The optimum number of clusters given by the integrated complete likelihood criterion is 47. The correspondence with the EFIGI classification is correct, but it appears that the Fisher-EM algorithm gives a great importance to the distribution of light which translates to characteristics such as the bulge to disc ratio, the inclination or the presence of foreground stars. The discrimination of some physical parameters (bulge-to-total luminosity ratio, (B–V)T, intrinsic diameter, presence of flocculence or dust, and arm strength) is very comparable in the two classifications.

Lack of Correlations between Cold Molecular Gas and AGN Properties in Type 1 AGNs at z ≲ 0.5

We present new NOrthern Extended Millimeter Array (NOEMA) observations of the CO(2–1) emission in eight of the brightest Palomar-Green quasars at z ≲ 0.5 to investigate the role of active galactic nucleus (AGN) feedback in luminous quasars detected at low redshifts. We detect CO(2–1) emission in three objects, from which we derive CO luminosities, molecular gas masses and fractions, and gas depletion times. In combination with data available in the literature, we build a total sample of 138 local type 1 AGNs with CO(2–1) measurements. We compare the AGN properties with the host galaxy molecular gas properties, considering systems nondetected in CO emission. We find that the CO luminosity does not correlate with AGN luminosity and Eddington ratio, while the molecular gas fraction is weakly correlated with Eddington ratio. The type 1 AGNs can be roughly separated into two populations in terms of infrared-to-CO luminosity ratio, with one population presenting values typically found in normal star-forming systems, while the other having lower ratio values, comparable to those measured for starbursts. We find no evidence that AGN feedback rapidly quenches star formation in type 1 AGNs. Our results may imply an underlying the role of host galaxy gravitational instabilities or the fast inflow of cold gas in triggering AGN activity.

Ionised gas outflows over the radio AGN life cycle

Feedback from active galactic nuclei (AGN) is known to affect the host galaxy’s evolution. In radio AGN, one manifestation of feedback is seen in gas outflows. However, it is still not well understood whether the effect of feedback evolves with the radio AGN life cycle. In this study, we aim to investigate this link using the radio spectral shape as a proxy for the evolutionary stage of the AGN. We used [O III] emission line spectra to trace the presence of outflows on the ionised gas. Using a sample of uniformly selected 129 radio AGN with L1.4 GHz ≈ 1023 − 1026 W Hz−1, and a mean stacking analysis of the [O III] profile, we conclude that the ionised gas outflow is linked to the radio spectral shape, and it evolves with the evolution of the radio source. We find that sources with a peak in their radio spectra (optically thick), on average, drive a broad outflow (FWHM ≈ 1330 ± 418 km s−1) with a velocity vout ≈ 240 km s−1. However, we detect no outflow in the stacked [O III] profile of sources without a peak in their radio spectrum (optically thin). We estimate a mass outflow rate of 0.09 − 0.41 M⊙ yr−1, and a kinetic power of 0.1 − 1.8 × 1041 erg s−1 for the outflow. In addition, we find that individual outflow detections are kinematically more extreme in peaked than non-peaked sources. We conclude that radio jets are most effective at driving gas outflows when young, and the outflow is typically short lived. Our stacking analysis shows no significant dependence of the presence of ionised gas outflows on the radio morphology, 1.4 GHz luminosity, optical luminosity and Eddington ratio of these sources. This suggests that in our sample, these properties do not play a defining role in driving the impact of the nuclear activity on the surrounding gas. We also identify candidate restarted AGN in our sample, whose [O III] profiles suggest that they have more disturbed gas kinematics than their evolved counterparts, although the evidence for this is tentative. Our findings support the picture where the impact of AGN feedback changes as the source evolves, and young radio jets interact with the ambient medium, clearing a channel of gas as they expand.

A High Fraction of Heavily X-Ray-obscured Active Galactic Nuclei

We present new estimates on the fraction of heavily X-ray-obscured, Compton-thick (CT) active galactic nuclei (AGNs) out to a redshift of z ≤ 0.8. From a sample of 540 AGNs selected by mid-infrared (MIR) properties in observed X-ray survey fields, we forward model the observed-to-intrinsic X-ray luminosity ratio () with a Markov Chain Monte Carlo simulation to estimate the total fraction of CT AGNs (f CT), many of which are missed in typical X-ray observations. We create model N H distributions and convert these to using a set of X-ray spectral models. We probe the posterior distribution of our models to infer the population of X-ray-nondetected sources. From our simulation we estimate a CT fraction of f CT = . We perform an X-ray stacking analysis for sources in Chandra X-ray Observatory fields and find that the expected soft (0.5–2 keV) and hard (2–7 keV) observed fluxes drawn from our model to be within 0.48 and 0.12 dex of our stacked fluxes, respectively. Our results suggests at least 50% of all MIR-selected AGNs, possibly more, are CT (N H ≳ 1024 cm−2), which is in excellent agreement with other recent work using independent methods. This work indicates that the total number of AGNs is higher than can be identified using X-ray observations alone, highlighting the importance of a multiwavelength approach. A high f CT also has implications for black hole (BH) accretion physics and supports models of BH and galaxy coevolution that include periods of heavy obscuration.

Shedding New Light on Weak Emission-line Quasars in the C iv–Hβ Parameter Space

Weak emission-line quasars (WLQs) are a subset of type 1 quasars that exhibit extremely weak Lyα + N v λ1240 and/or C iv λ1549 emission lines. We investigate the relationship between emission-line properties and accretion rate for a sample of 230 “ordinary” type 1 quasars and 18 WLQs at z < 0.5 and 1.5 < z < 3.5 that have rest-frame ultraviolet and optical spectral measurements. We apply a correction to the Hβ-based black hole mass (M BH) estimates of these quasars using the strength of the optical Fe ii emission. We confirm previous findings that WLQs’ M BH values are overestimated by up to an order of magnitude using the traditional broad-emission-line region size–luminosity relation. With this M BH correction, we find a significant correlation between Hβ-based Eddington luminosity ratios and a combination of the rest-frame C iv equivalent width and C iv blueshift with respect to the systemic redshift. This correlation holds for both ordinary quasars and WLQs, which suggests that the two-dimensional C iv parameter space can serve as an indicator of accretion rate in all type 1 quasars across a wide range of spectral properties.

A Chandra X-Ray Survey of Optically Selected Close Galaxy Pairs: Unexpectedly Low Occupation of Active Galactic Nuclei

High-resolution X-ray observations offer a unique tool for probing the still-elusive connection between galaxy mergers and active galactic nuclei (AGNs). We present an analysis of nuclear X-ray emission in an optically selected sample of 92 close galaxy pairs (with projected separations ≲20 kpc and line-of-sight velocity offsets <500 km s−1) at low redshift (), based on archival Chandra observations. The parent sample of galaxy pairs is constructed without imposing an optical classification of nuclear activity, thus it is largely free of selection effect for or against the presence of an AGN. Nor is this sample biased for or against gas-rich mergers. An X-ray source is detected in 70 of the 184 nuclei, giving a detection rate of , down to a 0.5–8 keV limiting luminosity of ≲1040 erg s−1. The detected and undetected nuclei show no systematic difference in their host galaxy properties such as galaxy morphology, stellar mass, and stellar velocity dispersion. When potential contamination from star formation is avoided (i.e., L 2−10 keV > 1041 erg s−1), the detection rate becomes (32/184), which shows no excess compared to the X-ray detection rate of a comparison sample of optically classified single AGNs. The fraction of pairs containing dual AGN is only . Moreover, most nuclei at the smallest projected separations probed by our sample (a few kiloparsecs) have an unexpectedly low apparent X-ray luminosity and Eddington ratio, which cannot be solely explained by circumnuclear obscuration. These findings suggest that close galaxy interaction is not a sufficient condition for triggering a high level of AGN activity.

Disk-corona modeling for spectral index and luminosity correlation of tidal disruption events

We present a relativistic disk-corona model for a steady state advective accretion disk to explain the UV to X-ray spectral index $\alpha_{\text{OX}}$ evolution of \textbf{four} tidal disruption event (TDE) sources XMMSL2J1446, XMMSL1J1404, XMMSL1J0740, \textbf{and AT2018fyk}. The viscous stress in our model depends on gas ($P_g$) and total ($P_t$) pressures as $\tau_{r\phi} \propto P_g^{\mu} P_t^{1-\mu}$, where $\mu$ is a constant. We compare various steady and time-dependent sub-Eddington TDE accretion models along with our disk-corona model to the observed $\alpha_{\text{OX}}$ of TDE sources and find that the disk-corona model agrees with the observations better than the other models. We find that $\mu$ is much smaller than unity for TDE sources XMMSL2J1446, XMMSL1J1404, and XMMSL1J0740. We also compare the relativistic model with a non-relativistic disk-corona model. The relativistic accretion dynamics reduce the spectral index relative to the non-relativistic accretion by increasing the energy transport to the corona. We estimate the mass accretion rate for all the sources and find that the observed luminosity follows a nearly linear relation with the mass accretion rate. The ratio of X-ray luminosity from the disk to the corona increases with the mass accretion rate. The observed $\alpha_{\text{OX}}$ shows positive and negative correlations with luminosity. The disk-corona model explains the negative correlation seen in the TDE sources XMMSL1J0740, XMMSL2J1446, and XMMSL1J1404. However, TDE AT2018fyk shows a positive correlation at higher luminosity and shows a better fit when a simple spherical adiabatic outflow model is added to the relativistic disk-corona model. Even though the disk luminosity dominates at a higher mass accretion rate, we show that the accretion models without a corona are unable to explain the observations, and the presence of a corona is essential.

A possible dwarf galaxy satellite-of-satellite problem in ΛCDM

Dark matter clusters on all scales, and it is therefore expected that even substructure should host its own substructure. Using the Extragalactic Distance Database, we searched for dwarf-galaxy satellites of dwarf galaxies, that is, satellite-of-satellite galaxies, corresponding to these substructures of substructure. From investigation of Hubble Space Telescope data for 117 dwarf galaxies, we report the discovery of a previously unknown dwarf galaxy around the ultra-diffuse M96 companion M96-DF6 at 10.2 Mpc in the Leo-I group. We confirm its dwarf-galaxy nature as a stellar overdensity. Modeling its structural parameters with a growth-curve analysis, we find that it is an ultrafaint dwarf galaxy with a luminosity of 1.5 × 105 L⊙, which is 135 times fainter than its host. Based on its close projection to M96-DF6, it is unlikely that their association occurs simply by chance. We compare the luminosity ratio of this and three other known satellite-of-satellite systems with results from two different cosmological sets of ΛCDM simulations. For the observed stellar mass range of the central dwarf galaxies, the simulated dwarfs have a higher luminosity ratio between the central dwarf and its first satellite (≈10 000) than observed (≈100), excluding the Large and Small Magellanic Cloud (LMC/SMC) system. No simulated dwarf analog at these observed stellar masses has the observed luminosity ratio. This cannot be due to missing resolution, because it is the brightest subhalos that are missing. This may indicate that there is a satellite-of-satellite (SoS) problem for ΛCDM in the stellar-mass range between 106 and 108 M⊙, the regime of the classical dwarf galaxies. However, simulated dwarf models at both a lower (&lt; 106 M⊙) and higher (&gt; 108 M⊙) stellar mass have comparable luminosity ratios. For the higher-stellar-mass systems, the LMC/SMC system is reproduced by simulations; for the lower stellar masses, no observed satellite-of-satellite system has been observed to date. More observations and simulations of satellite-of-satellite systems are needed to assess whether the luminosity ratio is at odds with ΛCDM.

SN 2017egm: A Helium-rich Superluminous Supernova with Multiple Bumps in the Light Curves

When discovered, SN 2017egm was the closest (redshift z = 0.03) hydrogen-poor superluminous supernova (SLSN-I) and a rare case that exploded in a massive and metal-rich galaxy. Thus, it has since been extensively observed and studied. We report spectroscopic data showing strong emission at around He i λ10830 and four He i absorption lines in the optical. Consequently, we classify SN 2017egm as a member of an emerging population of helium-rich SLSNe-I (i.e., SLSNe-Ib). We also present our late-time photometric observations. By combining them with archival data, we analyze high-cadence ultraviolet, optical, and near-infrared light curves spanning from early pre-peak (∼−20 days) to late phases (∼+300 days). We obtain its most complete bolometric light curve, in which multiple bumps are identified. None of the previously proposed models can satisfactorily explain all main light-curve features, while multiple interactions between the ejecta and circumstellar material (CSM) may explain the undulating features. The prominent infrared excess with a blackbody luminosity of 107–108 L ⊙ detected in SN 2017egm could originate from the emission of either an echo of a pre-existing dust shell or newly formed dust, offering an additional piece of evidence supporting the ejecta–CSM interaction model. Moreover, our analysis of deep Chandra observations yields the tightest-ever constraint on the X-ray emission of an SLSN-I, amounting to an X-ray-to-optical luminosity ratio ≲10−3 at late phases (∼100–200 days), which could help explore its close environment and central engine.

The First Photometric and Spectroscopic Studies of ASASSN-V J015428.67+204247.2 and its Relation to the Population of Low Mass Ratio Contact Binaries

We performed photometric, spectroscopic and orbital period investigations of ASASSN-V J015428.67+204247.2 (hereafter, J015428) for the first time. The light curves of VRI bands were obtained. Through the analysis of Wilson–Devinney program, J015428 was found as an A-subtype medium contact binary system with a low-mass ratio (q = 0.129, f = 26.8%). The atmospheric parameters were determined in spectroscopic analysis. In the orbital period investigations, we found that the orbital period of J015428 decreases at the rate of −7.13 × 10−8 day yr−1. And the long-term orbital period decrease is possibly due to angular momentum loss (AML). The absolute parameters was calculated with the photometric solutions and Gaia distance. Through the analyses of mass–radius and mass–luminosity diagrams of 54 contact binaries with the low mass ratios (0.096 ≤ q ≤ 0.15), the evolutionary states of low mass ratio binaries were investigated. The results by analyzing the energy transfer parameter indicated that energy transfer rate was a function of mass and bolometric luminosity ratio. We estimated the initial masses and the densities of two components and the age of the binary. The analysis of the orbital angular momentum supposed that J015428 may evolved from a short-period detached binary by AML. J015428 is in a stable contact stage at present.

Exploring the environment, magnetic fields, and feedback effects of massive high-redshift galaxies with [C II

Context. Massive galaxies are expected to grow through different transformative evolutionary phases. High-redshift starburst galaxies and quasars are thought to be such phases and thus provide insight into galaxy evolution. Several physical mechanisms are predicted to play an important role in driving these phases; for example, interaction with companion galaxies, active galactic nuclei feedback, and possibly magnetic fields. Aims. Our aim is to characterize the physical properties and the environment of the submillimeter galaxy AzTEC-3 at z = 5.3 and the lensed quasar BRI 0952−0115 at z = 4.4, and to set a limit on the polarization properties of the two sources. We intend to place these two sources in the broader context of galaxy evolution, specifically star formation and mass growth through cosmic time. Methods. We used full polarization, sub-arcsecond-resolution, ALMA band-7 observations of both BRI 0952−0115 and AzTEC-3. We detect [C II] (2P3/2−2P1/2) line emission towards both BRI 0952−0115 and AzTEC-3, along with companions in each field. We present an updated gravitational lensing model for BRI 0952−0115 for correction of gravitational magnification. Results. We present infrared luminosities, star-formation rates, and [C II] line to infrared luminosity ratios for each source. The [C II] emission line profile for both BRI 0952−0115 and AzTEC-3 exhibit a broad, complex morphology, indicating the possible presence of outflows. We present evidence of a “gas bridge” between AzTEC-3 and a companion source. Modified blackbody spectral energy distribution fitting is used to analyze the properties of [C II] detected companion sources in the field of both the submillimeter galaxy and the quasar. We investigated the possible role of the detected companions in outflow signatures. Using a simple dynamical mass estimate for the sources, we suggest that both systems are undergoing minor or major mergers. No polarization is detected for the [C II], placing an upper limit below that of theoretical predictions. Conclusions. Our results show that high-velocity wings are detected, indicating possible signs of massive outflows; however, the presence of companion galaxies can affect the final interpretation. Furthermore, the results provide additional evidence in support of the hypothesis that massive galaxies form in overdense regions, growing through minor or major mergers with companion sources. Finally, strong, ordered magnetic fields are unlikely to exist at the kiloparsec scale in the two studied sources.

Detections of [C ii] 158 μm and [O iii] 88 μm in a Local Lyman Continuum Emitter, Mrk 54, and Its Implications to High-redshift ALMA Studies* * Based on observations done with FIFI-LS on SOFIA.

We present integral field, far-infrared (FIR) spectroscopy of Mrk 54, a local Lyman continuum emitter, obtained with FIFI-LS on the Stratospheric Observatory for Infrared Astronomy. This is only the second time, after Haro 11, that [C ii] 158 μm and [O iii] 88 μm spectroscopy of the known LCEs have been obtained. We find that Mrk 54 has a strong [C ii] emission that accounts for ∼1% of the total FIR luminosity, whereas it has only moderate [O iii] emission, resulting in the low [O iii]/[C ii] luminosity ratio of 0.22 ± 0.06. In order to investigate whether [O iii]/[C ii] is a useful tracer of f esc (LyC escape fraction), we examine the correlations of [O iii]/[C ii] and (i) the optical line ratio of O32 ≡ [O iii] 5007 Å/[O ii] 3727 Å, (ii) specific star formation rate, (iii) [O iii] 88 μm/[O i] 63 μm ratio, (iv) gas-phase metallicity, and (v) dust temperature based on a combined sample of Mrk 54 and the literature data from the Herschel Dwarf Galaxy Survey and the LITTLE THINGS Survey. We find that galaxies with high [O iii]/[C ii] luminosity ratios could be the result of high ionization (traced by O32), bursty star formation, high ionized-to-neutral gas volume filling factors (traced by [O iii] 88 μm/[O i] 63 μm), and low gas-phase metallicities, which is in agreement with theoretical predictions. We present an empirical relation between the [O iii]/[C ii] ratio and f esc based on the combination of the [O iii]/[C ii] and O32 correlation, and the known relation between O32 and f esc. The relation implies that high-redshift galaxies with high [O iii]/[C ii] ratios revealed by the Atacama Large Millimeter/submillimeter Array may have f esc ≳ 0.1, significantly contributing to the cosmic reionization.

The ultraviolet habitable zone of exoplanets

ABSTRACT The dozens of rocky exoplanets discovered in the circumstellar habitable zone (CHZ) currently represent the most suitable places to host life as we know it outside the Solar system. However, the presumed presence of liquid water on the CHZ planets does not guarantee suitable environments for the emergence of life. According to experimental studies, the building blocks of life are most likely produced photochemically in presence of a minimum ultraviolet (UV) flux. On the other hand, high UV flux can be life-threatening, leading to atmospheric erosion and damaging biomolecules essential to life. These arguments raise questions about the actual habitability of CHZ planets around stars other than Solar-type ones, with different UV to bolometric luminosity ratios. By combining the ‘principle of mediocrity’ and recent experimental studies, we define UV boundary conditions (UV-habitable zone, UHZ) within which life can possibly emerge and evolve. We investigate whether exoplanets discovered in CHZs do indeed experience such conditions. By analysing Swift-UV/Optical Telescope data, we measure the near ultraviolet (NUV) luminosities of 17 stars harbouring 23 planets in their CHZ. We derive an empirical relation between NUV luminosity and stellar effective temperature. We find that 18 of the CHZ exoplanets actually orbit outside the UHZ, i.e. the NUV luminosity of their M-dwarf hosts is decisively too low to trigger abiogenesis – through cyanosulfidic chemistry – on them. Only stars with effective temperature ≳3900 K illuminate their CHZ planets with enough NUV radiation to trigger abiogenesis. Alternatively, colder stars would require a high-energy flaring activity.

MORPHOFIT: An automated galaxy structural parameters fitting package

In today’s modern wide-field galaxy surveys, there is the necessity for parametric surface brightness decomposition codes characterised by accuracy, small degree of user intervention, and high degree of parallelisation. We try to address this necessity by introducing MORPHOFIT, a highly parallelisable python package for the estimate of galaxy structural parameters. The package makes use of wide-spread and reliable codes, namely, SEXTRACTOR and GALFIT. It has been optimised and tested in both low-density and crowded environments, where blending and diffuse light makes the structural parameters estimate particularly challenging. MORPHOFIT allows the user to fit multiple surface brightness components to each individual galaxy, among those currently implemented in the code. Using simulated images of single Sérsic and bulge plus disk galaxy light profiles with different bulge-to-total luminosity (B/T) ratios, we show that MORPHOFIT is able to recover the input structural parameters of the simulated galaxies with good accuracy. We also compare its estimates against existing literature studies, finding consistency within the errors. We use the package in a companion paper to measure the structural parameters of cluster galaxies in order to study the wavelength dependence of the Kormendy relation of early-type galaxies. The package is available on github1 and on the Pypi server2.

Central molecular zones in galaxies: Multitransition survey of dense gas tracers HCN, HNC, and HCO+

New measurements of 46 nearby galaxy centers in up to three transitions of HCN, HNC, and HCO+ combined with literature surveys establish a database of 130 galaxies measured in both HCN and HCO+, and 94 galaxies in HNC as well, allowing a systematic exploration of the relations between normalized luminosities and line ratios. The almost linear relations between luminosities are predominantly caused by distance effects and do not reflect galaxy physical properties. Individual galaxies show significant dispersion in both their luminosity and line ratio, which will be analyzed in more detail in a later paper. Very few line ratios correlate either with luminosities or with other line ratios. Only the normalized transition ladders of HCN and HCO+ and the J = 1 − 0 12CO/13CO isotopologue ratio are positively correlated with CO and far infrared (FIR) luminosity. On average, HCN and HCO+ have very similar intensities and trace the same gas. In galaxies dominated by an active nucleus, HCO+ intensities appear to be depressed relative to HCN intensities. Only a small fraction of CO emission is associated with gas emitting in HCN and HCO+, yet a significant fraction of even that gas appears to be translucent molecular gas. In the observed galaxy centers, the HCN/CO line intensity ratio is not a proxy for the dense gas fraction, and the FIR/HCN and FIR/CO ratios are not proxies for the star formation efficiency. A proper understandig of star formation requires a more appropriate determination of gas mass than provided by the intensities of individual HCN or CO transitions. The observed molecular line emission is fully consistent with UV-photon heating boosted by significant mechanical heating. The molecular gas sampled by HCN and HCO+ has low kinetic temperatures Tkin = 10 − 50 K, low densities nH = 104 − 105 cm−3, and low optical depths in the ground-state lines. Most of the gas sampled by CO has densities lower by one to two orders of magnitude. For a mechanical heating fraction of 0.5, a modest energy input of only G = 300 G0 is required.

Updated Measurements of [O iii] 88 μm, [C ii] 158 μm, and Dust Continuum Emission from a z = 7.2 Galaxy

We present updated measurements of the [O iii] 88 μm, [C ii] 158 μm, and dust continuum emission from a star-forming galaxy at z = 7.212, SXDF-NB1006-2, by utilizing Atacama Large Millimeter/submillimeter Array (ALMA) archival data sets analysed in previous studies and data sets that have not been analysed before. The follow-up ALMA observations with higher angular resolution and sensitivity reveal a clumpy structure of the [O iii] emission on a scale of 0.32–0.85 kpc. We also combined all the ALMA [O iii] ([C ii]) data sets and updated the [O iii] ([C ii]) detection to 5.9σ (3.6σ–4.5σ). The non-detection of [C ii] with data from the REBELS large program implies the incompleteness of spectral-scan surveys using [C ii] to detect galaxies with high star formation rates (SFRs) but marginal [C ii] emission at high-z. The dust continuum at 90 and 160 μm remains undetected, indicating little dust content of <3.9 × 106 M ⊙ (3σ), and we obtained a more stringent constraint on the total infrared luminosity. We updated the [O iii]/[C ii] luminosity ratios to 10.2 ± 4.7 (6.1 ± 3.5) and 20 ± 12 (9.6 ± 6.1) for the 4.5σ and 3.6σ [C ii] detections, respectively, where the ratios in the parentheses are corrected for the surface brightness dimming effect on the extended [C ii] emission. We also found a strong [C ii] deficit (0.6–1.3 dex) between SXDF-NB1006-2 and the mean L [C II]−SFR relation of galaxies at 0 < z < 9.

Can we constrain galaxy geometry parameters using spatially integrated SED fitting?

ABSTRACT Sophisticated spectral energy distribution (SED) models describe dust attenuation and emission using geometry parameters. This treatment is natural since dust effects are driven by the underlying star–dust geometry in galaxies. An example is the starduster SED model, which divides a galaxy into a stellar disc, a stellar bulge, and a dust disc. This work utilizes the starduster SED model to study the efficacy of inferring geometry parameters using spatially integrated SED fitting. Our method fits the SED model to mock photometry produced by combining a semi-analytic model with the same SED model. Our fitting results imply that the disc radius can be constrained, while the inclination angle, dust disc to stellar disc radius ratio, bulge radius, and intrinsic bulge to total luminosity ratio are unconstrained, even though 21 filters from ultraviolet to far-infrared are used. We also study the impact of signal-to-noise (S/N) ratio, finding that the increase of S/N (up to 80) brings limited improvements to the results. We provide a detailed discussion to explain these findings, and point out the implications for models with more general geometry.

The Unusual AGN Host NGC 1266: Evidence for Shocks in a Molecular Gas Rich S0 Galaxy with a Low Luminosity Nucleus

NGC 1266 is a lenticular galaxy (S0) hosting an active galactic nucleus (AGN), and known to contain a large amount of shocked gas. We compare the luminosity ratio of mid-J CO lines to IR continuum with star-forming galaxies (SFGs), and then model the CO spectral line energy distribution (SLED). We confirm that in the mid- and high-J regions (J up = 4–13), the C-type shock (v s = 25 km s−1, n H = 5 × 104 cm−3) can reproduce the CO observations well. The galaxy spectral energy distribution (SED) is constructed and modeled by the code X-CIGALE and obtains a set of physical parameters including the star formation rate (SFR, 1.17 ± 0.47 M ⊙ yr−1). Also, our work provides SFR derivation of [C ii] from the neutral hydrogen regions only (1.38 ± 0.14 M ⊙yr−1). Previous studies have illusive conclusions on the AGN or starburst nature of the NGC 1266 nucleus. Our SED model shows that the hidden AGN in the system is intrinsically low-luminosity, consequently the infrared luminosity of the AGN does not reach the expected level. Archival data from NuSTAR hard X-ray observations in the 3–79 keV band shows a marginal detection, disfavoring presence of an obscured luminous AGN and implying that a compact starburst is more likely dominant for the NGC 1266 nucleus.