Browsing by Author "Armus, L."

Now showing 1 - 6 of 6
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    A 33GHz Survey of Local Major Mergers: Estimating the Sizes of the Energetically Dominant Regions from High-resolution Measurements of the Radio Continuum
    (2017) Barcos-Munoz, L.; Leroy, A. K.; Evans, A. S.; Condon, J.; Privon, G. C.; Thompson, T. A.; Armus, L.; Diaz-Santos, T.; Mazzarella, J. M.; Meier, D. S.; Momjian, E.; Murphy, E. J.; Ott, J.; Sanders, D. B.; Schinnerer, E.; Stierwalt, S.; Surace, J. A.; Walter, F.
    We present Very Large Array observations of the 33 GHz radio continuum emission from 22 local ultraluminous and luminous infrared (IR) galaxies (U/LIRGs). These observations have spatial (angular) resolutions of 30-720 pc (0.'' 07-0.'' 67) in a part of the spectrum that is likely to be optically thin. This allows us to estimate the size of the energetically dominant regions. We find half-light radii from 30 pc to 1.7 kpc. The 33 GHz flux density correlates well with the IR emission, and we take these sizes as indicative of the size of the region that produces most of the energy. Combining our 33 GHz sizes with unresolved measurements, we estimate the IR luminosity and star formation rate per area and the molecular gas surface and volume densities. These quantities span a wide range (4 dex) and include some of the highest values measured for any galaxy (e.g., Sigma(33 GHz)(SFR) <= 10(4.1) M-circle dot yr(-1) kpc(-2)) at least 13 sources appear Compton thick (N-H(33 GHz) >= 10(24) cm(-2)). Consistent with previous work, contrasting these data with observations of normal disk galaxies suggests a nonlinear and likely multivalued relation between star formation rate and molecular gas surface density, though this result depends on the adopted CO-to-H-2 conversion factor and the assumption that our 33 GHz sizes apply to the gas. Eleven sources appear to exceed the luminosity surface density predicted for starbursts supported by radiation pressure and supernova feedback; however, we note the need for more detailed observations of the inner disk structure. U/LIRGs with higher surface brightness exhibit stronger [C II] 158 mu m deficits, consistent with the suggestion that high energy densities drive this phenomenon.
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    A hard X-ray view of luminous and ultra-luminous infrared galaxies in GOALS - I. AGN obscuration along the merger sequence
    (2021) Ricci, C.; Privon, G. C.; Pfeifle, R. W.; Armus, L.; Iwasawa, K.; Torres-Albà, N.; Satyapal, S.; Bauer, F. E.; Treister, E.; Ho, L. C.; Aalto, S.; Arévalo, P.; Barcos-Muñoz, L.; Charmandaris, V.; Diaz-Santos, T.; Evans, A. S.; Gao, T.; Inami, H.; Koss, M. J.; Lansbury, G.; Linden, S. T.; Medling, A.; Sanders, D. B.; Song, Y.; Stern, D.; U, V.; Ueda, Y.; Yamada, S.
    The merger of two or more galaxies can enhance the inflow of material from galactic scales into the close environments of active galactic nuclei (AGNs), 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 AGNs that are Compton thick (CT;N-H >= 10(24)cm(-2) ) peaks at at a late merger stage, prior to coalescence, when the nuclei have projected separations (d(sep)) of 0.4-6 kpc. A similar peak is also observed in the median N-H [[(1.6 +/- 0.5) x 10(24) cm(-2)].]. The vast majority (85(-9)(+7) per cent)) of the AGNs in the final merger stages (d(sep) less than or similar to 10 kpc) are heavily obscured (N-H = 10(23) cm(-2)), and the median N-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 gas almost completely covering the AGN in late mergers. CT AGNs 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 (L2-10 less than or similar to 10(43) erg s(-1)) AGNs in U/LIRGs.
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    A Herschel/PACS Far-infrared Line Emission Survey of Local Luminous Infrared Galaxies
    (IOP PUBLISHING LTD, 2017) Diaz Santos, T.; Armus, L.; Charmandaris, V.; Lu, N.; Stierwalt, S.; Stacey, G.; Malhotra, S.; van der Werf, P. P.; Howell, J. H.; Privon, G. C.; Mazzarella, J. M.; Goldsmith, P. F.; Murphy, E. J.; Barcos Munoz, L.; Linden, S. T.; Inami, H.; Larson, L.; Evans, A. S.; Appleton, P.; Iwasawa, K.; Lord, S.; Sanders, D. B.; Surace, J. A.
    We present an analysis of [O I](63), [O III](88), [N II](122), and [C II](158) far-infrared (FIR) fine-structure line observations obtained with Herschel/PACS, for similar to 240 local luminous infrared galaxies (LIRGs) in the Great Observatories All-sky LIRG Survey. We find pronounced declines ("deficits") of line-to-FIR continuum emission for [N II](122), [O I](63), and [C II](158) as a function of FIR color and infrared luminosity surface density, Sigma(IR). The median electron density of the ionized gas in LIRGs, based on the [N II](122)/[N II](205) ratio, is n(e) = 41 cm(-3). We find that the dispersion in the [C II](158) deficit of LIRGs is attributed to a varying fractional contribution of photodissociation regions (PDRs) to the observed [C II](158) emission, f ([C II](158)(PDR)) = [C II](158)(PDR)/C II](158), which increases from similar to 60% to similar to 95% in the warmest LIRGs. The [O I](63)/[C II](158)(PDR) ratio is tightly correlated with the PDR gas kinetic temperaturein sources where [O I] 63 is not optically thick or self-absorbed. For each galaxy, we derive the average PDR hydrogen density, n(H), and intensity of the interstellar radiation field, G, in units of G(0) and find G/n(H) ratios of similar to 0.1-50 G(0) cm(3), with ULIRGs populating the upper end of the distribution. There is a relation between G/n(H) and Sigma(IR), showing a critical break at Sigma(IR)* similar or equal to 5 x 10(10) L-circle dot kpc(-2). Below Sigma(IR)*, G/n(H) remains constant, similar or equal to 0.32G(0) cm(3), and variations in Sigma(IR) are driven by the number density of star-forming regions within a galaxy, with no change in their PDR properties. Above Sigma(IR)*, G/n(H) increases rapidly with Sigma(IR), signaling a departure from the typical PDR conditions found in normal star-forming galaxies toward more intense/harder radiation fields and compact geometries typical of starbursting sources.
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    Massive Star Cluster Formation and Destruction in Luminous Infrared Galaxies in GOALS
    (IOP PUBLISHING LTD, 2017) Linden, S. T.; Evans, A. S.; Rich, J.; Larson, K. L.; Armus, L.; Diaz Santos, T.; Privon, G. C.; Howell, J.; Inami, H.; Kim, D. C.; Chien, L. H.; Vavilkin, T.; Mazzarella, J. M.; Modica, F.; Surace, J. A.; Manning, S.; Abdullah, A.; Blake, A.; Yarber, A.; Lambert, T.
    We present the results of a Hubble Space Telescope ACS/HRC FUV, ACS/WFC optical study into the cluster populations of a sample of 22 Luminous Infrared Galaxies in the Great Observatories All-Sky LIRG Survey. Through integrated broadband photometry, we have derived ages and masses for a total of 484 star clusters contained within these systems. This allows us to examine the properties of star clusters found in the extreme environments of LIRGs relative to lower luminosity star-forming galaxies in the local universe. We find that by adopting a Bruzual & Charlot simple stellar population model and Salpeter initial mass function, the age distribution of the clusters declines as dN/d tau = tau(-0.9+/-0.3), consistent with the age distribution derived for the Antennae Galaxies, and interpreted as evidence for rapid cluster disruption occurring in the strong tidal fields of merging galaxies. The large number of 10(6) M-circle dot young clusters identified in the sample also suggests that LIRGs are capable of producing more high-mass clusters than what is observed to date in any lower luminosity star-forming galaxy in the local universe. The observed cluster mass distribution of dN/dM = M-1.95+/-0.11 is consistent with the canonical -2 power law used to describe the underlying initial cluster mass function (ICMF) for a wide range of galactic environments. We interpret this as evidence against mass-dependent cluster disruption, which would flatten the observed CMF relative to the underlying ICMF distribution.
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    Molecular gas and dust properties of galaxies from the Great Observatories All-sky LIRG Survey
    (2019) Herrero-Illana, R.; Privon, G. C.; Evans, A. S.; Diaz-Santos, T.; Perez-Torres, M. A.; Alberdi, A.; Iwasawa, K.; Armus, L.; Aalto, S.; Mazzarella, J.; Chu, J.; Sanders, D. B.; Barcos-Munoz, L.; Charmandaris, V; Linden, S. T.; Yoon, I; Frayer, D. T.; Inami, H.; Kim, D-C; Borish, H. J.; Conway, J.; Murphy, E. J.; Song, Y.; Stierwalt, S.; Surace, J.
    We present IRAM-30 m Telescope (CO)-C-12 and (CO)-C-13 observations of a sample of 55 luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) in the local universe. This sample is a subset of the Great Observatory All-Sky LIRG Survey (GOALS), for which we use ancillary multi-wavelength data to better understand their interstellar medium and star formation properties. Fifty-three (96%) of the galaxies are detected in (CO)-C-12, and 29 (52%) are also detected in (CO)-C-13 above a 3 sigma level. The median full width at zero intensity (FWZI) velocity of the CO line emission is 661 km s(-1), and similar to 54% of the galaxies show a multi-peak CO profile. Herschel photometric data is used to construct the far-IR spectral energy distribution of each galaxy, which are fit with a modified blackbody model that allows us to derive dust temperatures and masses, and infrared luminosities. We make the assumption that the gas-to-dust mass ratio of (U)LIRGs is comparable to local spiral galaxies with a similar stellar mass (i.e., gas/dust of mergers is comparable to their progenitors) to derive a CO-to-H-2 conversion factor of = 1.8(-0.8)(+1.3) M-circle dot (K km s(-1) pc(2))(-1); such a value is comparable to that derived for (U)LIRGs based on dynamical mass arguments. We derive gas depletion times of 400 600 Myr for the (U)LIRGs, compared to the 1.3 Gyr for local spiral galaxies. Finally, we re-examine the relationship between the (CO)-C-12/(CO)-C-13 ratio and dust temperature, confirming a transition to elevated ratios in warmer systems.
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    Preparing for low surface brightness science with the Vera C. Rubin Observatory: Characterization of tidal features from mock images
    (2022) Martin, G.; Bazkiaei, A. E.; Spavone, M.; Iodice, E.; Mihos, J. C.; Montes, M.; Benavides, J. A.; Brough, S.; Carlin, J. L.; Collins, C. A.; Duc, P. A.; Gomez, F. A.; Galaz, G.; Hernandez-Toledo, H. M.; Jackson, R. A.; Kaviraj, S.; Knapen, J. H.; Martinez-Lombilla, C.; McGee, S.; O'Ryan, D.; Prole, D. J.; Rich, R. M.; Roman, J.; Shah, E. A.; Starkenburg, T. K.; Watkins, A. E.; Zaritsky, D.; Pichon, C.; Armus, L.; Bianconi, M.; Buitrago, F.; Busa, I; Davis, F.; Demarco, R.; Desmons, A.; Garcia, P.; Graham, A. W.; Holwerda, B.; Hon, D. S-H; Khalid, A.; Klehammer, J.; Klutse, D. Y.; Lazar, I; Nair, P.; Noakes-Kettel, E. A.; Rutkowski, M.; Saha, K.; Sahu, N.; Sola, E.; Vazquez-Mata, J. A.; Vera-Casanova, A.; Yoon, I
    Tidal features in the outskirts of galaxies yield unique information about their past interactions and are a key prediction of the hierarchical structure formation paradigm. The Vera C. Rubin Observatory is poised to deliver deep observations for potentially millions of objects with visible tidal features, but the inference of galaxy interaction histories from such features is not straightforward. Utilizing automated techniques and human visual classification in conjunction with realistic mock images produced using the NewHorizon cosmological simulation, we investigate the nature, frequency, and visibility of tidal features and debris across a range of environments and stellar masses. In our simulated sample, around 80 per cent of the flux in the tidal features around Milky Way or greater mass galaxies is detected at the 10-yr depth of the Legacy Survey of Space and Time (30-31 mag arcsec(-2)), falling to 60 per cent assuming a shallower final depth of 29.5 mag arcsec(-2). The fraction of total flux found in tidal features increases towards higher masses, rising to 10 per cent for the most massive objects in our sample (M-* similar to 10(11.5) M-circle dot). When observed at sufficient depth, such objects frequently exhibit many distinct tidal features with complex shapes. The interpretation and characterization of such features varies significantly with image depth and object orientation, introducing significant biases in their classification. Assuming the data reduction pipeline is properly optimized, we expect the Rubin Observatory to be capable of recovering much of the flux found in the outskirts of Milky Way mass galaxies, even at intermediate redshifts (z < 0.2).