arXiv subjects

Mark Gorski

Publications and source records attributed to Mark Gorski.

At least 19 recordsLinked to original sources

arXiv2026

ALMA Central Molecular Zone Exploration Survey (ACES) I: Overview

The mass flows and energy cycles within the inner regions of galaxies exert a powerful influence on the evolution of the galaxy population. The centre of the Milky Way is the only galactic nucleus for which it is possible to resolve the physical mechanisms that drive these cycles, namely star formation and feedback, while also tracing global (>100 pc) processes which determine where and when star formation and feedback occur. We present an overview of ACES, the 'Atacama Large Millimeter/submillimeter Array (ALMA) CMZ Exploration Survey', a ~1.5" angular resolution, 0.2-3 km/s spectral resolution ALMA Band 3 (85-102 GHz), survey of the 'Central Molecular Zone' (CMZ) -- the inner-100 pc of the Galaxy (l = 359.4 deg to 0.8 deg). ACES spectral setup is tuned to observe optimal tracers of the physical, chemical, and kinematic conditions in over 70 spectral features (e.g. HCO+, HNCO, SiO, H40alpha, complex molecules) of the gas in the CMZ, to derive the properties of all potentially star-forming Galactic Centre gas, from global scales (100 pc) to dense ~0.05 pc structures that are expected to host individual star-forming cores, down to sub-sonic (<0.4 km/s) velocity resolution. In this overview paper, we provide the scientific justification for the ACES survey, explain the choice of observational setup, and describe the data legacy products. Finally, we show some of the initial ACES data which highlight the power of ACES' combination of high angular resolution, unprecedented spatial dynamic range, sensitivity, spectral resolution and spectral bandwidth as an illustration of how ACES aims to understand how global processes set the location, intensity, and timescales for star formation and feedback in the CMZ.

astro-ph.GA↗

arXiv2025

The CO-to-H$_2$ conversion factor in the Milky Way's central parsec

Carbon monoxide (CO) emission is a widely used tracer of molecular hydrogen (H$_2$) in the interstellar medium (ISM), owing to its abundance, low excitation energy, and ease of detection in cold molecular environments, in contrast to $\mathrm{H}_2$ itself. While the CO-to-$\mathrm{H}_2$ conversion factor is often assumed to be constant across the disks of galaxies, deviations are observed in extreme environments such as the central molecular zone (CMZ) in galactic nuclei. Here we present the first estimate of the CO-to-$\mathrm{H}_2$ conversion factor on sub-kpc scales. We calculate CO-to-$\mathrm{H}_2$ conversion in the Milky Way's Circumnuclear Disk/Ring (CND/CNR) at $\sim 1$ pc radius around the Galactic Center black hole. We derive a conversion factor of $\alpha_\mathrm{CO} \simeq 4.5\pm2.5 \, M_\odot (\mathrm{K \, km \, s^{-1} pc^2})^{-1}$ or X[CO] $\simeq (2.1\pm1.1)\times 10^{20} \, \mathrm{cm}^{-2} (\mathrm{K \, km \, s^{-1}})^{-1}$. This value is consistent with the Galactic disk but higher than CMZ.

astro-ph.GA↗

arXiv2024

Components of star formation in NGC 253 : Non-negative Matrix Factorization Analysis with the ALCHEMI integrated intensity images

It is essential to examine the physical or chemical properties of molecular gas in starburst galaxies to reveal the underlying mechanisms characterizing starbursts. We used non-negative matrix factorization (NMF) to extract individual molecular or physical components involved in the star formation process in NGC\,253. We used images of 148 transitions from 44 different species of the ALMA large program ALCHEMI. Additionally, we included the continuum images at ALMA Bands 3 and 7 from the same dataset. For the five NMF components (NF1--5), we obtained that their distributions correspond to various basic phenomena related to star formation: i) low-density gas extended through the galactic central molecular zone (NF2), ii) shocks (NF3), iii) starburst regions (NF4), and iv) young star-forming regions (NF5). The other component (NF1) is related to excitation; three components obtained by NMF (NF3, 1, and 5) show a strong dependence upon the upper state energies of transitions, and represent low-, intermediate-, and high-excitation, respectively. We also compared our results using principal component analysis (PCA) previously applied to the same dataset. Molecular components extracted from NMF are similar to the ones obtained from PCA. However, NMF is better at extracting components associated with a single physical component, while a single component in PCA usually contains information on multiple physical components. This is especially true for features with weak intensities like emission from outflows. Our results suggest that NMF can be one of promising methods interpreting molecular line survey data, especially in the upcoming era of wide-band receivers.

astro-ph.GA↗

arXiv2024

A multiwavelength overview of the giant spiral UGC 2885

UGC 2885 (z = 0.01935) is one of the largest and most massive galaxies in the local Universe, yet its undisturbed spiral structure is unexpected for such an object and unpredicted in cosmological simulations. Understanding the detailed properties of extreme systems such as UGC 2885 can provide insight on the limits of scaling relations and physical processes driving galaxy evolution. Our goal is to understand whether UGC 2885 has followed a similar evolutionary path to other high-mass galaxies by examining its place on the fundamental metallicity relation and the star-forming main sequence. We present new observations of UGC 2885 with the CFHT and IRAM 30-m telescopes. These novel data are used to respectively calculate metallicity and molecular hydrogen mass values. We estimate stellar mass (M*) and star formation rate (SFR) based on mid-infrared observations with the Wide-field Infrared Survey Explorer. We find global metallicities Z = 9.28, 9.08 and 8.74 at the 25 kpc ellipsoid from N2O2, R23 and O3N2 indices, respectively. This puts UGC 2885 at the high end of the galaxy metallicity distribution. The molecular hydrogen mass is calculated as M(H2)=(1.89+/-0.24)e11 Msun, the SFR as 1.63+/-0.72 Msun/yr and the stellar mass as (4.83 +/- 1.52)e11 Msun, which gives a star formation efficiency (SFE = SFR/M(H2)) of (8.67+/-4.20)e12/yr. This indicates that UGC 2885 has an extremely high molecular gas content when compared to known samples of star forming galaxies (~100 times more) and a relatively low SFR for its current gas content. We conclude that UGC 2885 has gone through cycles of star formation periods, which increased its stellar mass and metallicity to its current state. The mechanisms that are fueling the current molecular gas reservoir and keeping the galaxy from producing stars remain uncertain. We discuss the possibility that a molecular bar is quenching star forming activity.

astro-ph.GA↗

arXiv2024

The fountain of the luminous infrared galaxy Zw049.057 as traced by its OH megamaser

High resolution (0."037-0."13 [10-35 pc]) e-MERLIN ($\lambda6-18$ cm) and (0."024 [6.5 pc]) ALMA ($\lambda 1.1$ mm) observations have been used to image OH (hydroxyl) and H$_2$CO (formaldehyde) megamaser emission, and HCN 3->2 emission towards the nuclear (<100 pc) region of the luminous infrared galaxy Zw049.057. Zw049.057 hosts a compact obscured nucleus (CON), thus representing a class of galaxies that are often associated with inflow and outflow motions. Formaldehyde megamaser emission is detected towards the nuclear region, <30 pc (<0."1), and traces a structure along the disk major axis. OH megamaser (OHM) emission is detected along the minor axis of the disk, ~30 pc (0."1) from the nucleus, where it exhibits a velocity gradient with extrema of -20 km/s south-east (SE) of the disk and -110 km/s north-west (NW) of the disk. HCN 3->2 emission reveals extended emission, along the disk minor axis out to ~60 pc (0."2). Analysis of the minor axis HCN emission reveals high-velocity features, extending out to 600 km/s, redshifted on the SE side and blueshifted on the NW side. We propose that the high-velocity HCN emission traces a fast >250 km/s and collimated outflow, that is enveloped by a wide-angle and slow ~50 km/s outflow that is traced by the OHM emission. Analysis of the outflow kinematics suggests that the slow wide-angle outflow will not reach escape velocity and instead will fall back to the galaxy disk, evolving as a so-called fountain flow, while the fast collimated outflow traced by HCN emission will likely escape the nuclear region. We suggest that the absence of OHM emission in the nuclear region is due to high densities there. Even though OHMs associated with outflows are an exception to conventional OHM emission, we expect them to be common in CON sources that host both OHM and H$_2$CO megamasers.

astro-ph.GA↗

arXiv2023

SUNRISE: The rich molecular inventory of high-redshift dusty galaxies revealed by broadband spectral line surveys

Understanding the nature of high-$z$ dusty galaxies requires a comprehensive view of their ISM and molecular complexity. However, the molecular ISM at high-$z$ is commonly studied using only a few species beyond CO, limiting our understanding. In this paper, we present the results of deep 3 mm spectral line surveys using the NOEMA targeting two lensed dusty galaxies: APM 08279+5255 (APM), a quasar at redshift $z=3.911$, and NCv1.143 (NC), a $z=3.565$ starburst galaxy. The spectral line surveys cover rest-frame frequencies from about 330-550 GHz. We report the detection of 38 and 25 emission lines in APM and NC, respectively. The spectra reveal the chemical richness and the complexity of the physical properties of the ISM. By comparing the spectra of the two sources and combining the gas excitation analysis, we find that the physical properties and the chemical imprints of the ISM are different between them: the molecular gas is more excited in APM, exhibiting higher molecular-gas temperatures and densities compared to NC; the chemical abundances in APM are akin to the values of local AGN, showing boosted relative abundances of the dense gas tracers that might be related to high-temperature chemistry and/or XDRs, while NC more closely resembles local starburst galaxies. The most significant differences are found in H2O, where the 448GHz H2O line is significantly brighter in APM, likely linked to the intense far-infrared radiation from the dust powered by AGN. Our astrochemical model suggests that at such high column densities, FUV radiation is less important in regulating the ISM, while CRs (X-rays/shocks) are the key players in shaping the abundance of the molecules and the initial conditions of star formation. Such deep spectral line surveys open a new window to study the physical and chemical properties of the ISM and the radiation field of galaxies in the early Universe. (abridged)

astro-ph.GA↗

arXiv2023

5-12 pc resolution ALMA imaging of gas and dust in the obscured compact nucleus of IRAS 17578-0400

We here present 0.02-0.04'' resolution ALMA observation of the compact obscured nucleus (CON) of IRAS17578-0400. A dusty torus within the nucleus, approximately 4 pc in radius, has been uncovered, exhibiting a usually flat spectral index at ALMA band 3, likely due to the millimeter corona emission from the central supermassive black hole (SMBH). The dense gas disk, traced by $^{13}$CO(1-0), spans 7 pc in radius and suggests an outflow driven by a disk wind due to its asymmetrical structure along the minor axis. Collimated molecular outflows (CMO), traced by the low-velocity components of the HCN(3-2) and HCO$^+$(3-2) lines, align with the minor axis gas disk. Examination of position-velocity plots of HCN(3-2) and HCO$^+$(3-2) reveals a flared dense gas disk extended a radius of $\sim$ 60 pc, infalling and rotating at speeds of about 200 km/s and 300 km/s, respectively. A centrifugal barrier, located around 4 pc from the dynamical center, implies an SMBH mass of approximately 10$^8$ $M_\odot$, consistent with millimeter corona emission estimates. The CMO maintains a steady rotation speed of 200 km/s over the 100 pc scale along the minor axis. The projected speed of the CMO is about 80 km/s, corresponding to around $\sim$ 500 km/s, assuming an inclination angle of 80$^\circ$. Such a kinematics structure of disk-driven collimated rotating molecular outflow with gas supplies from a falling rotating disk indicates that the feedback of the compact obscured nucleus is likely regulated by the momentum transfer of the molecular gas that connects to both the feeding of the nuclear starburst and supermassive black hole.

astro-ph.GA↗

arXiv2022

The Morpho-Kinematic Architecture of Super Star Clusters in the Center of NGC253

The center of the nearby galaxy NGC\,253 hosts a population of more than a dozen super star clusters (SSCs) which are still in the process of forming. The majority of the star formation of the burst is concentrated in these SSCs, and the starburst is powering a multiphase outflow from the galaxy. In this work, we measure the 350~GHz dust continuum emission towards the center of NGC\,253 at 47~milliarcsecond (0.8 pc) resolution using data from the Atacama Large Millimeter/submillimeter Array (ALMA). We report the detection of 350~GHz (dust) continuum emission in the outflow for the first time, associated with the prominent South-West streamer. In this feature, the dust emission has a width of $\approx$~8~pc, is located at the outer edge of the CO emission, and corresponds to a molecular gas mass of $\sim~(8-17)\times10^6$~M$_\odot$. In the starburst nucleus, we measure the resolved radial profiles, sizes, and molecular gas masses of the SSCs. Compared to previous work at somewhat lower spatial resolution, the SSCs here break apart into smaller substructures with radii $0.4-0.7$~pc. In projection, the SSCs, dust, and dense molecular gas appear to be arranged as a thin, almost linear, structure roughly 155~pc in length. The morphology and kinematics of this structure can be well explained as gas following $x_2$ orbits at the center of a barred potential. We constrain the morpho-kinematic arrangement of the SSCs themselves, finding that an elliptical, angular momentum-conserving ring is a good description of the both morphology and kinematics of the SSCs.

astro-ph.GA↗

arXiv2021

ALMA Imaging of a Galactic Molecular Outflow in NGC4945

We present the ALMA detection of molecular outflowing gas in the central regions of NGC4945, one of the nearest starbursts and also one of the nearest hosts of an active galactic nucleus (AGN). We detect four outflow plumes in CO (3-2) at ~0.3" resolution that appear to correspond to molecular gas located near the edges of the known ionized outflow cone and its (unobserved) counterpart behind the disk. The fastest and brightest of these plumes has emission reaching observed line-of-sight projected velocities of over 450 km/s beyond systemic, equivalent to an estimated physical outflow velocity v>600 km/s for the fastest emission. Most of these plumes have corresponding emission in HCN or HCO+ (4-3). We discuss a kinematic model for the outflow emission where the molecular gas has the geometry of the ionized gas cone and shares the rotation velocity of the galaxy when ejected. We use this model to explain the velocities we observe, constrain the physical speed of the ejected material, and account for the fraction of outflowing gas that is not detected due to confusion with the galaxy disk. We estimate a total molecular mass outflow rate dMmol/dt~20 Msun/yr flowing through a surface within 100 pc of the disk midplane, likely driven by a combination of the central starburst and AGN.

astro-ph.GA↗

arXiv2021

Discovery of Methanimine Megamasers Toward Compact Obscured Galaxy Nuclei

We present the first search for the 5.29 GHz methanimine($\rm{CH}_2\rm{NH}$) $1_{10}-1_{11}$ transition toward a sample of galaxy nuclei. We target seven galaxies that host Compact Obscured Nuclei (CONs) with the Karl G. Jansky Very Large Array. These galaxies are characterized by Compton-thick cores. $\rm{CH}_2\rm{NH}$ emission is detected toward six CONs. The brightness temperatures measured toward Arp220 indicate maser emission. Isotropic luminosities of the $\rm{CH}_2\rm{NH}$ transition, from all sources where it is detected, exceed 1 L$_{\odot}$ and thus may be considered megamasers. We also detect formaldehyde ($\rm{H}_2\rm{CO}$) emission toward three CONs. The isotropic $\rm{CH}_2\rm{NH}$ luminosities are weakly correlated with the infrared luminosity of the host galaxy and strongly correlated with OH megamaser luminosities from the same galaxies. Non-LTE radiative transfer models suggest that the maser is pumped by the intense mm/submm radiation field of the CONs. Our study suggests that $\rm{CH}_2\rm{NH}$ megamasers are linked to the nuclear processes within 100 pc of the Compton Thick nucleus within CONs.

astro-ph.GA↗

arXiv2021

Outflows from Super Star Clusters in the Central Starburst of NGC253

Young massive clusters play an important role in the evolution of their host galaxies, and feedback from the high-mass stars in these clusters can have profound effects on the surrounding interstellar medium. The nuclear starburst in the nearby galaxy NGC253 at a distance of 3.5 Mpc is a key laboratory in which to study star formation in an extreme environment. Previous high resolution (1.9 pc) dust continuum observations from ALMA discovered 14 compact, massive super star clusters (SSCs) still in formation. We present here ALMA data at 350 GHz with 28 milliarcsecond (0.5 pc) resolution. We detect blueshifted absorption and redshifted emission (P-Cygni profiles) towards three of these SSCs in multiple lines, including CS 7$-$6 and H$^{13}$CN 4$-$3, which represents direct evidence for previously unobserved outflows. The mass contained in these outflows is a significant fraction of the cluster gas masses, which suggests we are witnessing a short but important phase. Further evidence of this is the finding of a molecular shell around the only SSC visible at near-IR wavelengths. We model the P-Cygni line profiles to constrain the outflow geometry, finding that the outflows must be nearly spherical. Through a comparison of the outflow properties with predictions from simulations, we find that none of the available mechanisms completely explains the observations, although dust-reprocessed radiation pressure and O star stellar winds are the most likely candidates. The observed outflows will have a very substantial effect on the clusters' evolution and star formation efficiency.

astro-ph.GA↗

arXiv2020

Super Star Clusters in the Central Starburst of NGC 4945

NGC 4945 is a nearby (3.8 Mpc) galaxy hosting a nuclear starburst and Seyfert Type 2 AGN. We use the Atacama Large Millimeter/submillimeter Array (ALMA) to image the 93 GHz (3.2 mm) free-free continuum and hydrogen recombination line emission (H40$α$ and H42$α$) at 2.2 pc (0.12'') resolution. Our observations reveal 27 bright, compact sources with FWHM sizes of 1.4 - 4.0 pc, which we identify as candidate super star clusters. Recombination line emission, tracing the ionizing photon rate of the candidate clusters, is detected in 15 sources, 6 of which have a significant synchrotron component to the 93 GHz continuum. Adopting an age of ~5 Myr, the stellar masses implied by the ionizing photon luminosities are $\log_{10}$($M_{\star}$/M$_{\odot}$) $\approx$ 4.7 - 6.1. We fit a slope to the cluster mass distribution and find $β= -1.8 \pm 0.4$. The gas masses associated with these clusters, derived from the dust continuum at 350 GHz, are typically an order of magnitude lower than the stellar mass. These candidate clusters appear to have already converted a large fraction of their dense natal material into stars and, given their small free-fall times of ~0.05 Myr, are surviving an early volatile phase. We identify a point-like source in 93 GHz continuum emission which is presumed to be the AGN. We do not detect recombination line emission from the AGN and place an upper limit on the ionizing photons which leak into the starburst region of $Q_0 < 10^{52}$ s$^{-1}$.

astro-ph.GA↗

arXiv2019

The molecular outflow in NGC253 at a resolution of two parsecs

We present 0.15'' (~2.5pc) resolution ALMA CO(3-2) observations of the starbursting center in NGC253. Together with archival ALMA CO(1-0) and CO(2-1) data we decompose the emission into a disk and non-disk component. We find ~7-16% of the CO luminosity to be associated with the non-disk component ($1.2-4.2 \times 10^7$ K km s$^{-1}$ pc$^2$). The total molecular gas mass in the center of NGC253 is $\sim 3.6 \times 10^8$ M$_\odot$ with $\sim 0.5 \times 10^8$ M$_\odot$ (~15%) in the non-disk component. These measurements are consistent across independent mass estimates through three CO transitions. The high-resolution CO(3-2) observations allow us to identify the molecular outflow within the non-disk gas. Using a starburst conversion factor, we estimate the deprojected molecular mass outflow rate, kinetic energy and momentum in the starburst of NGC253. The deprojected molecular mass outflow rate is in the range ~14-39 M$_\odot$ yr$^{-1}$ with an uncertainty of 0.4dex. The large spread arises due to different interpretations of the kinematics of the observed gas while the errors are due to unknown geometry. The majority of this outflow rate is contributed by distinct outflows perpendicular to the disk, with a significant contribution by diffuse molecular gas. This results in a mass loading factor $η= \dot{M}_\mathrm{out} / \dot{M}_\mathrm{SFR}$ in the range $η\sim 8-20$ for gas ejected out to ~300pc. We find the kinetic energy of the outflow to be $\sim 2.5-4.5 \times 10^{54}$ erg and ~0.8dex typical error which is ~0.1% of the total or ~8% of the kinetic energy supplied by the starburst. The outflow momentum is $4.8-8.7 \times 10^8$ M$_\odot$ km s$^{-1}$ (~0.5dex error) or ~2.5-4% of the kinetic momentum released into the ISM by feedback. The unknown outflow geometry and launching sites are the primary source of uncertainty in this study.

astro-ph.GA↗

arXiv2018

Diagnostics of a Nuclear Starburst: Water and Methanol Masers

We test models of starburst driven outflows using observations of the 22.2 GHz H$_2$O and 36.2 GHz class I CH$_3$OH maser lines. We have observed the starburst galaxy NGC 253 using the Karl G. Jansky Very Large Array. We present evidence for entrainment of star-forming dense-molecular gas in the outflow of NGC 253. We also show that H$_2$O masers are associated with forming super star clusters and not with supernova remnants. We detect four new 36 GHz CH$_3$OH masers in the central kpc and show possible evidence for a star-formation origin of two class I CH$_3$OH masers. Such high resolution observations are essential for understanding the origin of these masers.

astro-ph.GA↗

arXiv2018

Forming Super Star Clusters in the Central Starburst of NGC 253

NGC 253 hosts the nearest nuclear starburst. Previous observations show a region rich in molecular gas, with dense clouds associated with recent star formation. We used ALMA to image the 350 GHz dust continuum and molecular line emission from this region at 2 pc resolution. Our observations reveal ~14 bright, compact (~2-3 pc FWHM) knots of dust emission. Most of these sources are likely to be forming super star clusters (SSCs) based on their inferred dynamical and gas masses, association with 36 GHz radio continuum emission, and coincidence with line emission tracing dense, excited gas. One source coincides with a known SSC, but the rest remain invisible in Hubble near-infrared (IR) imaging. Our observations imply that gas still constitutes a large fraction of the overall mass in these sources. Their high brightness temperature at 350 GHz also implies a large optical depth near the peak of the IR spectral energy distribution. As a result, these sources may have large IR photospheres and the IR radiation force likely exceeds L/c. Still, their moderate observed velocity dispersions suggest that feedback from radiation, winds, and supernovae are not yet disrupting most sources. This mode of star formation appears to produce a large fraction of stars in the burst. We argue for a scenario in which this phase lasts ~1 Myr, after which the clusters shed their natal cocoons but continue to produce ionizing photons. The strong feedback that drives the observed cold gas and X-ray outflows likely occurs after the clusters emerge from this early phase.

astro-ph.GA↗

arXiv2018

Survey of Water and Ammonia in Nearby galaxies (SWAN): Resolved Ammonia Thermometry, and Water and Methanol Masers in IC 342, NGC 6946 and NGC 2146

The Survey of Water and Ammonia in Nearby galaxies (SWAN) studies atomic and molecular species across the nuclei of four star forming galaxies: NGC\,253, IC\,342, NGC\,6946, and NGC\,2146. As part of this survey, we present Karl G. Jansky Very Large Array (VLA) molecular line observations of three galaxies: IC\,342, NGC\,6946 and NGC\,2146. NGC\,253 is covered in a previous paper. These galaxies were chosen to span an order of magnitude in star formation rates and to select a variety of galaxy types. We target the metastable transitions of ammonia NH$_{3}$(1,1) to (5,5), the 22\,GHz water (H$_2$O) ($6_{16}-5_{23}$) transition, and the 36.1\,GHz methanol (CH$_3$OH) ($4_{-1}-3_{0}$) transition. {We use the NH$_{3}$\ metastable lines to perform thermometry of the dense molecular gas.} We show evidence for uniform heating across the central kpc of IC\,342 with two temperature components for the molecular gas, similar to NGC 253,} of 27\,K and 308\,K, and that the dense molecular gas in NGC\,2146 has a temperature $<$86 K. We identify two new water masers in IC\,342, and one new water maser in each of NGC\,6946 and NGC\,2146. The two galaxies NGC\,253 and NGC\,2146, with the most vigorous star formation, host H$_2$O kilomasers. Lastly, we detect the first 36\,GHz CH$_3$OH\ masers in IC\,342 and NGC\,6946. For the four external galaxies the total CH$_3$OH\ luminosity in each galaxy suggests a correlation with galactic star formation rate, whereas the morphology of the emission is similar to that of HNCO, a weak shock tracer.

astro-ph.GA↗

arXiv2017

Survey of Water and Ammonia in Nearby galaxies (SWAN): Resolved Ammonia Thermometry, Water and Methanol Masers in the Nuclear Starburst of NGC 253

We present Karl G Jansky Very Large Array molecular line observations of the nearby starburst galaxy NGC 253, from SWAN: "Survey of Water and Ammonia in Nearby galaxies". SWAN is a molecular line survey at centimeter wavelengths designed to reveal the physical conditions of star forming gas over a range of star forming galaxies. NGC 253 has been observed in four 1GHz bands from 21 to 36 GHz at 6" ($\sim100$pc) spatial and 3.5 km s$^{-1}$ spectral resolution. In total we detect 19 transitions from seven molecular and atomic species. We have targeted the metastable inversion transitions of ammonia (NH$_{3}$) from (1,1) to (5,5) and the (9,9) line, the 22.2 GHz water (H$_2$O) ($6_{16}-5_{23}$) maser, and the 36.1 GHz methanol (CH$_3$OH) ($4_{-1}-3_{0}$) maser. Utilizing NH$_{3}$ as a thermometer, we present evidence for uniform heating over the central kpc of NGC 253. The molecular gas is best described by a two kinetic temperature model with a warm 130K and a cooler 57K component. A comparison of these observations with previous ALMA results suggests that the molecular gas is not heated in photon dominated regions or shocks. It is possible that the gas is heated by turbulence or cosmic rays. In the galaxy center we find evidence for NH$_{3}$(3,3) masers. Furthermore we present velocities and luminosities of three water maser features related to the nuclear starburst. We partially resolve CH$_3$OH masers seen at the edges of the bright molecular emission, which coincides with expanding molecular superbubbles. This suggests that the masers are pumped by weak shocks in the bubble surfaces.

astro-ph.GA↗

arXiv2011

X-rays from Blue Compact Dwarf Galaxies

We measured the X-ray fluxes from an optically-selected sample of blue compact dwarf galaxies (BCDs) with metallicities <0.07 and solar distances less than 15 Mpc. Four X-ray point sources were observed in three galaxies, with five galaxies having no detectable X-ray emission. Comparing X-ray luminosity and star formation rate, we find that the total X-ray luminosity of the sample is more than 10 times greater than expected if X-ray luminosity scales with star formation rate according to the relation found for normal-metallicity star-forming galaxies. However, due to the low number of sources detected, one can exclude the hypothesis that the relation of the X-ray binaries to SFR in low-metalicity BCDs is identical to that in normal galaxies only at the 96.6% confidence level. It has recently been proposed that X-ray binaries were an important source of heating and reionization of the intergalactic medium at the epoch of reionization. If BCDs are analogs to unevolved galaxies in the early universe, then enhanced X-ray binary production in BCDs would suggest an enhanced impact of X-ray binaries on the early thermal history of the universe.

astro-ph.GA↗