Jack W. Sulentic

The AMIGA sample of isolated galaxies - IX. Molecular gas properties

Aims. We characterize the molecular gas content (ISM cold phase) using CO emission of a redshift-limited subsample of isolated galaxies from the AMIGA (Analysis of the interstellar Medium of Isolated GAlaxies) project in order to provide a comparison sample for studies of galaxies in different environments. Methods. We present the 12 CO(1–0) data for 273 AMIGA galaxies, most of them (n = 186) from our own observations with the IRAM 30 m and the FCRAO 14 m telescopes and the rest from the literature. We constructed a redshift-limited sample containing galaxies with 1500 km s −1 <v< 5000 km s −1 and excluded objects with morphological evidence of possible interaction. This sample (n = 173) is the basis for our statistical analysis. It contains galaxies with molecular gas masses, MH2 , in the range of ∼10 8 −10 10 M� .I t is dominated, both in absolute number and in detection rate, by spiral galaxies of type T = 3–5 (Sb-Sc). Most galaxies were observed with a single pointing towards their centers. Therefore, we performed an extrapolation to the total molecular gas mass expected in the entire disk based on the assumption of an exponential distribution. We then studied the relationships between MH2 and other galactic properties (LB, D 2 , LK, LFIR ,a ndMHI). Results. We find correlations between MH2 and LB, D 2 , LK ,a ndLFIR. The tightest correlation of MH2 holds with LFIR and, for T = 3– 5, with LK, and the poorest with D 2 . The correlations with LFIR and LK are very close to linearity. The correlation with LB is nonlinear so that MH2 /LB increases with LB. The molecular and the atomic gas masses of our sample show no strong correlation. We find a low mean value, log(MH2 /MHI) = −0.7 (for T = 3–5), and a strong decrease in this ratio with morphological type. The molecular gas column density and the surface density of the star formation rate (the Kennicutt-Schmidt law) show a tight correlation with a rough unity slope. We compare the relations of MH2 with LB and LK found for AMIGA galaxies to samples of interacting galaxies from the literature and find an indication for an enhancement of the molecular gas in interacting galaxies of up to 0.2–0.3 dex.

Broad-line region physical conditions along the quasar eigenvector 1 sequence

We compare broad emission-line profiles and estimate line ratios for all major emission lines between Lyα and Hβ in a sample of six quasars. The sources were chosen with two criteria in mind: the existence of high-quality optical and ultraviolet spectra and the possibility of sampling the spectroscopic diversity in the 4D eigenvector 1 (4DE1) context. In the latter sense, each source occupies a region (bin) in the full width at half-maximum (FWHM)(Hβ) versus Fe II opt strength plane that is significantly different from the others. High signal-to-noise ratio Hβ emission-line profiles are used as templates for modelling the other lines (Lyα, CIVλ1549, He IIλ1640, Al IIIλ1860, Si III]λ1892 and Mg IIλ2800). We can adequately model all broad lines assuming the existence of three components distinguished by blueshifted, unshifted and redshifted centroids [indicated as a blue component (BLUE), broad component (BC) and very broad component (VBC), respectively]. BC (electron density n e ~10 12 cm -3 , ionization parameter U ~10 -2 and column density N c ≃ 10 23 cm -2 ) is present in almost all type-1 quasars and therefore corresponds most closely to the classical broad-line emitting region (the reverberating component). The bulk of Mg IIλ2800 and Fe II emission also arises in this region. The BLUE emission (log n e ~ 10, log U ~ -1 and log N c < 23) arises in less optically thick gas; it is often thought to arise in an accretion disc wind. The least understood component involves the VBC (high ionization and large column density), which is found in no more than half (but almost all radio-loud) type-1 quasars and luminous Seyfert nuclei. It is perhaps the most distinguishing characteristic of quasars with FWHM (Hβ) ≳ 4000 km s -1 that belong to the so-called population B of our 4DE1 space. Population A quasars [FWHM (Hβ) ≲ 4000 km s -1 ] are dominated by BC emission in Hβ and BLUE component emission in CIVλ1549 and other high ionization lines. 4DE1 appears to be the most useful current context for revealing and unifying spectral diversity in type-1 quasars.

Highly accreting quasars: sample definition and possible cosmological implications

We propose a method to identify quasars radiating closest to the Eddington limit, defining primary and secondary selection criteria in the optical, UV and X-ray spectral range based on the 4D eigenvector 1 formalism. We then show that it is possible to derive a redshift-independent estimate of luminosity for extreme Eddington ratio sources. Using preliminary samples of these sources in three redshift intervals (as well as two mock samples), we test a range of cosmological models. Results are consistent with concordance cosmology but the data are insufficient for deriving strong constraints. Mock samples indicate that application of the method proposed in this paper using dedicated observations would allow to set stringent limits on Omega_M and significant constraints on Omega_Lambda.

The AMIGA sample of isolated galaxies XI. Optical characterisation of nuclear activity

Context. This paper is part of a series involving the AMIGA project (Analysis of the Interstellar Medium of Isolated GAlaxies), which identifies and studies a statistically significant sample of the most isolated galaxies in the northern sky. Aims. We present a catalogue of nuclear activity, traced by optical emission lines, in a well-defined sample of the most isolated galaxies in the local Universe, which will be used as a basis for studying the effect of the environment on nuclear activity. Methods. We obtained spectral data from the 6th Data Release of the Sloan Digital Sky Survey, which were inspected in a semiautomatic way. We subtracted the underlying stellar populations from the spectra (using the software Starlight) and modelled the nuclear emission features. Standard emission-line diagnostics diagrams were applied, using a new classification scheme that takes into account censored data, to classify the type of nuclear emission. Results. We provide a final catalogue of spectroscopic data, stellar populations, emission lines and classification of optical nuclear activity for AMIGA galaxies. The prevalence of optical active galactic nuclei (AGN) in AMIGA galaxies is 20.4%, or 36.7% including transition objects. The fraction of AGN increases steeply towards earlier morphological types and higher luminosities. We compare these results with a matched analysis of galaxies in isolated denser environments (Hickson Compact Groups). After correcting for the effects of the morphology and luminosity, we find that there is no evidence for a difference in the prevalence of AGN between isolated and compact group galaxies, and we discuss the implications of this result. Conclusions. We find that a major interaction is not a necessary condition for the triggering of optical AGN.

The AMIGA sample of isolated galaxies - X. A first look at isolated galaxy colors

Context. The basic properties of galaxies can be affected by both nature (internal processes) or nurture (interactions and effects of environment). Deconvolving the two effects is an important current effort in astrophysics. Observed properties of a sample of isolated galaxies should be mainly the result of internal (natural) evolution. It follows that nurture–induced galaxy evolution can only be understood through a comparative study of galaxies in different environments. Aims. We take a first look at SDSS (g − r) colors of galaxies in the AMIGA sample, which consists of many of the most isolated galaxies in the local Universe. This alerted us at the same time to the pitfalls of using automated SDSS colors. Methods. We focused on median values for the principal morphological subtypes found in the AMIGA sample (E/S0 and Sb-Sc) and compared them with equivalent measures obtained for galaxies in denser environments. Results. We find a weak tendency for AMIGA spiral galaxies to be redder than objects in close pairs. We find no clear difference when we compared this with galaxies in other (e.g. group) environments. However, the (g − r) color of isolated galaxies shows a Gaussian distribution, as might be expected assuming nurture-free evolution. We find a smaller median absolute deviation in colors for isolated galaxies compared to both wide and close pairs. The majority of the deviation on median colors for spiral subtypes is caused by a color-luminosity correlation. Surprisingly, isolated and non-isolated early-type galaxies show similar (g −r). We see little evidence for a green valley in our sample because most spirals redder than (g − r) = 0.7 have spurious colors. Conclusions. The redder colors of AMIGA spirals and lower color dispersions for AMIGA subtypes – compared with close pairs – are likely caused by a more passive star formation in very isolated galaxies.

DUST EMISSION AND STAR FORMATION IN STEPHAN'S QUINTET

We analyze a comprehensive set of MIR/FIR observations of Stephans Quintet (SQ), taken with the Spitzer Space Telescope. Our study reveals the presence of a luminous (L_(IR) ≈ 4.6 × 10^(43) erg s^(-1)) and extended component of infrared dust emission, not connected with the main bodies of the galaxies, but roughly coincident with the X-ray halo of the group. We fitted the inferred dust emission spectral energy distribution of this extended source and the other main infrared emission components of SQ, including the intergalactic shock, to elucidate the mechanisms powering the dust and polycyclic aromatic hydrocarbon emission, taking into account collisional heating by the plasma and heating through UV and optical photons. Combining the inferred direct and dust-processed UV emission to estimate the star formation rate (SFR) for each source we obtain a total SFR for SQ of 7.5 M_☉ yr^(-1), similar to that expected for non-interacting galaxies with stellar mass comparable to the SQ galaxies. Although star formation in SQ is mainly occurring at, or external to the periphery of the galaxies, the relation of SFR per unit physical area to gas column density for the brightest sources is similar to that seen for star formation regions in galactic disks. We also show that available sources of dust in the group halo can provide enough dust to produce up to L_(IR) ≈ 10^(42) erg s^(-1) powered by collisional heating. Though a minority of the total infrared emission (which we infer to trace distributed star-formation), this is several times higher than the X-ray luminosity of the halo, so could indicate an important cooling mechanism for the hot intergalactic medium (IGM) and account for the overall correspondence between FIR and X-ray emission. We investigate two potential modes of star formation in SQ consistent with the data, fueled either by gas from a virialized hot IGM continuously accreting onto the group, whose cooling is enhanced by grains injected from an in situ population of intermediate mass stars, or by interstellar gas stripped from the galaxies. The former mode offers a natural explanation for the observed baryon deficiency in the IGM of SQ as well as for the steep L_(X)-T_(X) relation of groups such as SQ with lower velocity dispersions.

The stellar mass–size relation for the most isolated galaxies in the local Universe

Disentangling processes governing the formation and evolution of galaxies is a fundamental challenge in extragalactic research. In this sense t he current belief that galaxies grow by the action of minor mergers makes the study of the stellar mass‐size relation in different environments an important tool for distinguishing effects of internal and external processes. The aim of this work is to study the effects of environment on the growth in size of galaxies. As part of AMIGA project (Analysis of the Interstellar Medium of Isolated GAlaxies), we examine the stellar mass‐size relation for a sample of the most isolated galaxies in the local Universe interpreted as stellar systems where evolution has been mainly governed by internal processes. Effects of environment on the stellar mass‐size relation are evaluated by comparing our results with samples of less isolated early‐ and late‐type galaxies, as well as, for the first time, di fferent spiral subtypes. Stellar masses in our sample were derived by fitting the SED of each galaxy with kcorrect. We used two different size estimators, the half‐light radius obtained with .. .. .. .. .. .. .. .. .. .. .. ! ,

On the molecular gas content and SFR in Hickson Compact Groups: enhanced or deficient? ⋆

Aims. We study the effect of the extreme environment in Hickson Compact groups (HCGs) on the molecular gas mass, MH2 , and the star formation rate (SFR) of galaxies as a function of atomic hydrogen (HI) content and evolutionary phase of the group. Methods. We have selected a redshift limited (D<100 Mpc) sample of 88 galaxies in 20 HCGs with available atomic hydrogen (HI) VLA maps, covering a wide range of HI deficiencies and evoluti onary phases of the groups, and containing at least one spiral galaxy. We derived the far-infrared (FIR) luminosity (LFIR) from IRAS data and used it as a tracer of the star formation rate (SFR). We calculated the HI mass (MHI), LFIR and MH2 deficiencies. Results. The mean deficiencies of LFIR and MH2 of spiral galaxies in HCGs are close to 0, indicating that the ir average SFR and molecular gas content are similar to those of isolated galaxies. However, there are indications of an excess in MH2 (∼ 50%) in spiral galaxies in HCGs which can be interpreted, assuming that there is no systematic difference in the CO-to-H2 conversion factor, as either an enhanced molecular gas content or as a higher concentration of the molecular component towards the center in comparison to galaxies in lower density environments. In contrast, the mean MHI of spiral galaxies in HCGs is only 12% of the expected value. The specific star formation rate (sSFR = SFR/stellar mass) tends to be lower for galaxies with a higher MH2 or MHI deficiency. This trend is not seen for the star formation effi ciency (SFE=SFR/MH2), which is very similar to isolated galaxies. We found tentative indications for an enhancement of MH2 in spiral galaxies in HCGs in an early evolutionary phase and a decrease in later phases. We suggest that this might be due to an enhancement of the conversion from atomic to molecular gas due to on-going tidal interactions in an early evolutionary phase, followed by HI stripping and a decrease of the molecular gas content because of lack of replenishment. Conclusions. The properties of MH2 and LFIR in galaxies in HCGs are surprisingly similar to those of isol ated galaxies, in spite of the much higher def(MHI) of the former. The trends of the sSFR and def(MH2 ) with def(MHI) and the evolutionary state indicate, however, that the ongoing interaction might have some effect on the molecular gas and SF.

The AMIGA sample of isolated galaxies VIII. The rate of asymmetric H i profiles in spiral galaxies

(abridged) Measures of the HI properties of a galaxy are among the most sensitive interaction diagnostic at our disposal. We report here on a study of HI profile asymmetries (e.g., lopsidedness) in a sample of some of the most isolated galaxies in the local Universe. This presents us with an excellent opportunity to quantify the range of intrinsic HI asymmetries and provides us with a zero-point calibration for evaluating these measurements in less isolated samples. We characterize the HI profile asymmetries and search for correlations between HI asymmetry and their environments, as well as their optical and far infrared (FIR) properties. We use high signal-to-noise global HI profiles for galaxies in the AMIGA project (this http URL). We restrict our study to N=166 galaxies with accurate measures of the HI shape properties. We quantify asymmetries using a flux ratio parameter. The asymmetry parameter distribution of our isolated sample is well described by a Gaussian model. The width of the distribution is sigma=0.13, and could be even smaller (sigma=0.11) if instrumental errors are reduced. Only 2% of our carefully vetted isolated galaxies sample show an asymmetry in excess of 3sigma. By using this sample we minimize environmental effects as confirmed by the lack of correlation between HI asymmetry and tidal force (one-on-one interactions) and neighbor galaxy number density. On the other hand, field galaxy samples show wider distributions and deviate from a Gaussian curve. As a result we find higher asymmetry rates (~10-20%) in such samples. We find evidence that the spiral arm strength is inversely correlated with the HI asymmetry. We also find an excess of FIR luminous galaxies with larger HI asymmetries that may be spirals associated with hidden accretion events. Our sample presents the smallest fraction of asymmetric HI profiles compared with any other yet studied.

ARE (PSEUDO)BULGES IN ISOLATED GALAXIES ACTUALLY PRIMORDIAL RELICS

We present structural parameters and (g – i) bulge/disk colors for a large sample (189) of isolated AMIGA galaxies. The structural parameters of bulges were derived from the two-dimensional bulge/disk/bar decomposition of Sloan Digital Sky Survey i-band images using GALFIT. Galaxies were separated between classical bulges (nb > 2.5) and pseudobulges (nb < 2.5), resulting in a dominant pseudobulge population (94%) with only 12 classical bulges. In the μ e -R e plane, pseudobulges are distributed below the elliptical relation (smaller R e and fainter μ e ), with the closest region to the Kormendy relation populated by those pseudobulges with larger values of B/T. We derived (g – i) bulge colors using aperture photometry and find that pseudobulges show median colors (g – i) b ~ 1.06, while their associated disks are much bluer, (g – i) d ~ 0.77. Moreover, 64% (113/177) of pseudobulges follow the red sequence of early-type galaxies. Bluer pseudobulges tend to be located in galaxies with the highest likelihood of tidal perturbation. The red bulge colors and low B/T values for AMIGA isolated galaxies are consistent with an early formation epoch and not much subsequent growth. Properties of bulges in isolated galaxies contrast with a picture where pseudobulges grow continuously via star formation. They also suggest that environment could be playing a role in rejuvenating the pseudobulges.