Shocked POststarburst Galaxy Survey II: The Molecular Gas Content and Properties of a Subset of SPOGs (original) (raw)
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There are many mechanisms by which galaxies can transform from blue, star-forming spirals to red, quiescent early-type galaxies, but our current census of them does not form a complete picture. Recent studies of nearby case studies seem to have identified a population of galaxies that quench “quietly.” Traditional poststarburst searches seem to catch galaxies only after they have quenched and transformed, and thus miss any objects with additional ionization mechanisms exciting the remaining gas. The Shocked POststarburst Galaxy Survey (SPOGS) aims to identify galaxies in an earlier phase of transformation, in which the nebular lines are excited via shocks instead of through star formation processes. Utilizing the Oh-Sarzi-Schawinski-Yi (OSSY) measurements on the Sloan Digital Sky Survey Data Release 7 catalog, we applied Balmer absorption and shock boundary criteria to identify 1,067 SPOG candidates (SPOGs*) within z = 0.2. SPOGs* represent 0.7% of emission line galaxies (and 0.2% of the OSSY sample galaxies, similar to the poststarburst fraction). SPOGs* colors suggest that they are in an earlier phase of transition than traditionally selected poststarburst galaxies. Quenching timescales are consistent with shock dissipation timescales. SPOGs* have a 13% 1.4 GHz detection rate from the Faint Images of the Radio Sky at Twenty centimeters survey, higher than most other subsamples, and comparable only to low-ionization nuclear emission line region hosts, suggestive of the presence of AGNs. SPOGs* also have stronger Na I D absorption than predicted from the stellar population, suggestive of interstellar winds. It appears that SPOGs* represent an earlier phase in galaxy transformation than traditionally selected poststarburst galaxies, and that a large proportion of SPOGs* also have properties consistent with disruption of their interstellar media, a key component to galaxy transformation. It is likely that many of the known pathways to transformation undergo a SPOG phase. Studying this sample of SPOGs* further, including their morphologies, active galactic nuclei properties, and environments, has the potential for us to build a more complete picture of the initial conditions that can lead to a galaxy evolving by finding galaxies previously not identified as transforming.
Shocked POststarburst Galaxy Survey. III. The Ultraviolet Properties of SPOGs
The Astrophysical Journal
The Shocked POststarburst Galaxy Survey (SPOGS) aims to identify galaxies in the transitional phase between actively star-forming and quiescence with nebular lines that are excited from shocks rather than star formation processes. We explored the ultraviolet (UV) properties of objects with near-ultraviolet (NUV) and far-ultraviolet (FUV) photometry from archival GALEX data; 444 objects were detected in both bands, 365 in only the NUV, and 24 in only the FUV, for a total of 833 observed objects. We compared SPOGs to samples of star-forming galaxies (SFs), quiescent galaxies (Qs), classical E+A post-starburst galaxies, active galactic nuclei (AGN) host galaxies, and interacting galaxies. We found that SPOGs have a larger range in their FUV-NUV and NUV-r colors compared with most of the other samples, although all of our comparison samples occupied color space inside of the SPOGs region. On the basis of their UV colors, SPOGs are a heterogeneous group, possibly made up of a mixture of SFs, Qs, and/or AGN. Using Gaussian mixture models, we are able to recreate the distribution of FUV-NUV colors of SPOGs and E+A galaxies with different combinations of SFs, Qs, and AGN. We find that the UV colors of SPOGs require a >60% contribution from SFs, with either Qs or AGN representing the remaining contribution, while UV colors of E+A galaxies required a significantly lower fraction of SFs, supporting the idea that SPOGs are at an earlier point in their transition from quiescent to star-forming than E+A galaxies.
Nearby early-type galaxies with ionized gas
Astronomy & Astrophysics, 2011
A large fraction of early-type galaxies (ETGs) shows emission lines in their optical spectra, mostly with LINER characteristics. Despite the number of studies, the nature of the ionization mechanisms is still debated. Many ETGs also show several signs of rejuvenation episodes. Aims. We aim to investigate the ionization mechanisms and the physical processes of a sample of ETGs using mid-infrared spectra. Methods. We present here low resolution Spitzer-IRS spectra of 40 ETGs, 18 of which from our proposed Cycle 3 observations, selected from a sample of 65 ETGs showing emission lines in their optical spectra. We homogeneously extract the mid-infrared (MIR) spectra, and after the proper subtraction of a "passive" ETG template, we derive the intensity of the ionic and molecular lines and of the polycyclic aromatic hydrocarbon (PAH) emission features. We use MIR diagnostic diagrams to investigate the powering mechanisms of the ionized gas.
CO excitation in the Seyfert galaxy NGC 34: stars, shock or AGN driven?
Monthly Notices of the Royal Astronomical Society, 2017
We present a detailed analysis of the X-ray and molecular gas emission in the nearby galaxy NGC 34, to constrain the properties of molecular gas, and assess whether, and to what extent, the radiation produced by the accretion on to the central black hole affects the CO line emission. We analyse the CO spectral line energy distribution (SLED) as resulting mainly from Herschel and ALMA data, along with X-ray data from NuSTAR and XMM-Newton. The X-ray data analysis suggests the presence of a heavily obscured active galactic nucleus (AGN) with an intrinsic luminosity of L 1-100 keV 4.0 × 10 42 erg s −1. ALMA high-resolution data (θ 0.2 arcsec) allow us to scan the nuclear region down to a spatial scale of ≈100 pc for the CO(6-5) transition. We model the observed SLED using photodissociation region (PDR), X-ray-dominated region (XDR), and shock models, finding that a combination of a PDR and an XDR provides the best fit to the observations. The PDR component, characterized by gas density log(n/cm −3) = 2.5 and temperature T = 30 K, reproduces the low-J CO line luminosities. The XDR is instead characterized by a denser and warmer gas (log(n/cm −3) = 4.5, T = 65 K), and is necessary to fit the high-J transitions. The addition of a third component to account for the presence of shocks has been also tested but does not improve the fit of the CO SLED. We conclude that the AGN contribution is significant in heating the molecular gas in NGC 34.
Molecular gas in NUclei of GAlaxies (NUGA) XIII. The interacting Seyfert 2/LINER galaxy NGC 5953
Astronomy and Astrophysics, 2010
We present 12 CO(1-0) and 12 CO(2-1) maps of the interacting Seyfert 2/LINER galaxy NGC 5953 obtained with the IRAM interferometer at resolutions of 2. ′′ 1 × 1. ′′ 4 and 1. ′′ 1 × 0. ′′ 7, respectively. We also present single-dish IRAM 30 m observations of the central region of NGC 5953 for the 12 CO(1-0), 12 CO(2-1), and HCN(1-0) transitions at resolutions of 22 ′′ , 12 ′′ , and 29 ′′ , respectively. The CO emission is distributed over a disk of diameter ∼16 ′′ (∼2.2 kpc), within which are several, randomly distributed peaks. The strongest peak does not coincide with the nucleus, but is instead offset from the center, ∼2-3 ′′ (∼340 pc) toward the west/southwest. The kinematics of the molecular component are quite regular, as is typical of a rotating disk. We also compared the 12 CO distribution of NGC 5953 with observations at other wavelengths in order to study correlations between different tracers of the interstellar medium. The HST/F606W WFPC2 images show flocculent spiral structures and an "S-shape" feature > ∼ 60 pc in radius, possibly associated with a nuclear bar or with the radio jet. A two-dimensional bulge/disk decomposition of the H-band (HST/F160W) and 3.6 µm (Spitzer/IRAC) images reveals a circumnuclear "ring" ∼10-14 ′′ in diameter, roughly coincident in size with the CO disk and with a star-forming ring previously identified in ionized gas. This ring is not present in the near-infrared (NIR) J − K color image, nor is it present in the "dust-only" image constructed from the 8 µm IRAC map. The implication is that the excess residual ring is stellar, with colors similar to the surrounding disk. We interpret this ring, visible in ionized gas, which appears as stars in the NIR, and with no sign of hot dust, as due to a red super giant population at least 10-15 Myr old. However, star formation is still ongoing in the disk and in the ring itself. Using NIR images, we computed the gravity torques exerted by the stellar potential on the gas. The torques are predominantly positive in both 12 CO(1-0) and 12 CO(2-1), suggesting that gas is not flowing into the center, and less than 5% of the gas angular momentum is exchanged in each rotation. This comes from the regular and almost axisymmetric total mass and gas distributions in the center of the galaxy. In NGC 5953, the AGN is apparently not being actively fueled in the current epoch.
Molecular gas in NUclei of GAlaxies (NUGA)
Astronomy and Astrophysics, 2009
We present CO(1-0) and CO(2-1) maps of the LINER galaxy NGC 7217, obtained with the IRAM interferometer, at 2.4 ′′ ×1.9 ′′ and 1.2 ′′ ×0.8 ′′ resolution respectively. The nuclear ring (at r = 12 ′′ = 0.8kpc) dominates the CO maps, and has a remarkable sharp surface density gradient at its inner edge. The latter is the site of the stellar/Hα ring, while the CO emission ring extends farther or is broader (500-600pc). This means that the star formation has been more intense toward the inner edge of the CO ring, in a thin layer, just at the location of the high gas density gradient. The CO(2-1)/CO(1-0) ratio is close to 1, typical of warm optically thick gas with high density. The overall morphology of the ring is quite circular, with no evidence of non-circular velocities. In the CO(2-1) map, a central concentration might be associated with the circumnuclear ionized gas detected inside r=3" and interpreted as a polar ring in the literature. The CO(2-1) emission inside 3" coincides with a spiral dust lane, clearly seen in the HST V − I color image. N-body simulations including gas dissipation and star formation are performed to better understand the nature of the nuclear ring observed. The observed rotation curve of NGC 7217 allows two possibilities, according to the adopted mass for the disk:
Molecular Gas Properties of Galaxies: The SMA CO(2-1) B0DEGA Legacy Project
Galaxies and their Masks, 2010
In the last two decades high resolution (< 5 ′′ ) CO observations for ∼ 150 galaxies have provided a wealth of information about the molecular gas morphologies in the circumnuclear regions. While in samples of 'normal' galaxies the molecular gas does not seem to peak toward the nuclear regions for about 50% of the galaxies, barred galaxies and mergers show larger concentrations. However, we do not exactly know from an observational point of view how the molecular gas properties of a galaxy evolve as a result of an interaction. Here we present the SMA CO(2-1) B0DEGA (Below 0 DEgree GAlaxies) legacy project in which we are imaging the CO(2-1) line of the circumnuclear regions (1 ′ ) of a large (∼ 70) sample of nearby IR-bright spiral galaxies, likely interacting, and that still remained unexplored due to its location in the southern hemisphere. We find different molecular gas morphologies, such as rings, nuclear arms, nuclear bars and asymmetries. We find a centrally peaked concentration in about 85% of the galaxies with typical size scales of about 0.5 -1 kpc. This might be related to perturbations produced by recent interactions.
A Search for Very Extended Ionized Gas in Nearby Starburst and Active Galaxies
The Astronomical Journal, 2003
We report the results from a pilot study of 10 nearby starburst and active galaxies conducted with the Taurus Tunable Filter (TTF) on the Anglo-Australian and William Herschel Telescopes. The main purpose of this imaging survey is to search for warm emission-line gas on the outskirts (galactocentric distances R 10 kpc) of galaxies to provide direct constraints on the size and geometry of the "zone of influence" of these galaxies on their environment. Gaseous complexes or filaments larger than ∼ 20 kpc are discovered or confirmed in six of the galaxies in the sample (NGC 1068, NGC 1482, NGC 4388, NGC 6240, NGC 7213, and MR 2251-178). Slightly smaller structures are seen for the first time in the ionization cones and galactic winds of NGC 1365, NGC 1705, Circinus galaxy, and ESO484-G036. The TTF data are combined with new optical long-slit spectra as well as published and archived radio and X-ray maps to constrain the origin and source of ionization of these filaments. A broad range of phenomena is observed, including large-scale ionization cones and galactic winds, tidal interaction, and ram-pressure stripping by an intracluster medium. The source of ionization in this gas ranges from shock ionization to photoionization by the central AGN or in-situ hot young stars. The sample is too small to draw statistically meaningful conclusions about the extent and properties of the warm ionized medium on large scale and its relevance to galaxy formation and evolution. The next generation of tunable filters on large telescopes promises to improve the sensitivity to faint emission-line fluxes at least tenfold and allow systematic surveys of a large sample of emission-line galaxies.
The Astronomical Journal, 2001
We present new CO (1 − 0) observations of eleven extragalactic tails and bridges in nine interacting galaxy systems, almost doubling the number of such features with sensitive CO measurements. Eight of these eleven features were undetected in CO to very low CO/HI limits, with the most extreme case being the NGC 7714/5 bridge. This bridge contains luminous H II regions and has a very high HI column density (1.6 × 10 21 cm −2 in the 55 ′′ CO beam), yet was undetected in CO to rms T R * = 2.4 mK. The HI column density is higher than standard H 2 and CO self-shielding limits for solar-metallicity gas, suggesting that the gas in this bridge is metal-poor and has an enhanced N H 2 /I CO ratio compared to the Galactic value. Only one of the eleven features in our sample was unambiguously detected in CO, a luminous HI-rich star formation region near an optical tail in the compact group Stephan's Quintet. We detect CO at two widely separated velocities in this feature, at ∼6000 km s −1 and ∼6700 km s −1 . Both of these components have HI and Hα counterparts. These velocities correspond to those of galaxies in the group, suggesting that this gas is material that has been removed from two galaxies in the group. The CO/HI/Hα ratios for both components are similar to global values for spiral galaxies.