Studying the atomic gas (HI) properties of the most isolated galaxies is
essential to quantify the effect that the environment exerts on this sensitive
component of the interstellar medium. We observed and compiled HI data for a
well defined sample of ~ 800 galaxies in the Catalog of Isolated Galaxies, as
part of the AMIGA project (Analysis of the ISM in Isolated GAlaxies,
http://amiga.iaa.es), which enlarges considerably previous samples used to
quantify the HI deficiency in galaxies located in denser environments. By
studying the shape of 182 HI profiles, we revisited the usually accepted result
that, independently of the environment, more than half of the galaxies present
a perturbed HI disk. In isolated galaxies this would certainly be a striking
result if these are supposed to be the most relaxed systems, and has
implications in the relaxation time scales of HI disks and the nature of the
most frequent perturbing mechanisms in galaxies. Our sample likely exhibits the
lowest HI asymmetry level in the local Universe. We found that other field
samples present an excess of ~ 20% more asymmetric HI profiles than that in
CIG. Still a small percentage of galaxies in our sample present large
asymmetries. Follow-up high resolution VLA maps give insight into the origin of
such asymmetries.Comment: 4 pages, 2 figures, Conference 'Galaxies in Isolation: Exploring
  Nature vs. Nurture', Granada, 12-15 May 2009. To be published in the ASP
  Conference Serie

Athanassoula, E.

Bosma, A.

Espada, D.

Huchtmeier, W. K.

Leon, S.

Lisenfeld, U.

Sabater, J.

Sulentic, J.

Verdes-Montenegro, L.

Verley, S.

Yun, M.

English

arXiv

International conference “Galaxies in Isolation: Exploring Nature vs. Nurture” held in Granada (Spain), May 12–15, 2009.Studying the atomic gas (HI) properties of the most isolated galaxies is essential to quantify the effect that the environment exerts on this sensitive component of the interstellar medium. We observed and compiled HI data for a well defined sample of ~ 800 galaxies in the Catalog of Isolated Galaxies, as part of the AMIGA project (Analysis of the ISM in Isolated GAlaxies, this http URL), which enlarges considerably previous samples used to quantify the HI deficiency in galaxies located in denser environments. By studying the shape of 182 HI profiles, we revisited the usually accepted result that, independently of the environment, more than half of the galaxies present a perturbed HI disk. In isolated galaxies this would certainly be a striking result if these are supposed to be the most relaxed systems, and has implications in the relaxation time scales of HI disks and the nature of the most frequent perturbing mechanisms in galaxies. Our sample likely exhibits the lowest HI asymmetry level in the local Universe. We found that other field samples present an excess of ~ 20% more asymmetric HI profiles than that in CIG. Still a small percentage of galaxies in our sample present large asymmetries. Follow-up high resolution VLA maps give insight into the origin of such asymmetries.This work has been partially supported by Spanish
DGI grant AYA2008-06181-C02, as well as Junta de Andalucia (Spain) grants
P08-FQM-4205-PEX and TIC-114 16-C02-01. DE is supported by the Marie Curie International fellowship MOIF-CT-2006-40298

Espada Fernández, Daniel

Lisenfeld , Ute

Verley, Simon

Yun, M. S.

Repositorio Institucional Universidad de Granada

Setting the normalcy level of HI properties in isolated galaxies

Studying the atomic gas (HI) properties of the most isolated galaxies is essential to quantify the effect that the environment exerts on this sensitive component of the interstellar medium.  We observed and compiled HI data for a well defined sample of ∼ 800 galaxies in the Catalog of Isolated Galaxies, as part of the AMIGA project (Analysis of the ISM in Isolated GAlaxies, http://amiga.iaa.es), which enlarges considerably previous samples used to quantify the HI deficiency in galaxies located in denser environments. By studying the shape of 182 HI profiles, we revisited the usually accepted result that, independently of the environment, more than half of the galaxies present a perturbed HI disk. In isolated galaxies this would certainly be a striking result if these are supposed to be the most relaxed systems, and has implications in the relaxation time scales of HI disks and the nature of the most frequent perturbing mechanisms in galaxies.  Our sample likely exhibits the lowest HI asymmetry level in the local Universe. We found that field samples present an excess of ∼ 20% more asymmetric HI profiles than those in CIG. Still a small percentage of galaxies in our sample present large asymmetries. Follow-up high resolution VLA maps give insight into the origin of such asymmetries

Espada, D

Verdes-Montenegro, L

Athanassoula, E

Bosma, A

Huchtmeier, WK

Leon, S

Lisenfeld, U

Sabater, J

Sulentic, J

Verley, S

Yun, Min

ScholarWorks@UMass Amherst

University of Massachusetts AmherstScholarWorks@UMass AmherstAstronomy Department Faculty Publication Series Astronomy2010Setting the Normalcy Level of HI Properties inIsolated GalaxiesD EspadaL Verdes-MontenegroE AthanassoulaA BosmaWK HuchtmeierSee next page for additional authorsFollow this and additional works at: https://scholarworks.umass.edu/astro_faculty_pubsPart of the Astrophysics and Astronomy CommonsThis Article is brought to you for free and open access by the Astronomy at ScholarWorks@UMass Amherst. It has been accepted for inclusion inAstronomy Department Faculty Publication Series by an authorized administrator of ScholarWorks@UMass Amherst. For more information, pleasecontact scholarworks@library.umass.edu.Recommended CitationEspada, D; Verdes-Montenegro, L; Athanassoula, E; Bosma, A; Huchtmeier, WK; Leon, S; Lisenfeld, U; Sabater, J; Sulentic, J; Verley,S; and Yun, Min, "Setting the Normalcy Level of HI Properties in Isolated Galaxies" (2010). Astronomical Society of the PacificConference Series. 1122.Retrieved from https://scholarworks.umass.edu/astro_faculty_pubs/1122AuthorsD Espada, L Verdes-Montenegro, E Athanassoula, A Bosma, WK Huchtmeier, S Leon, U Lisenfeld, J Sabater, JSulentic, S Verley, and Min YunThis article is available at ScholarWorks@UMass Amherst: https://scholarworks.umass.edu/astro_faculty_pubs/1122arXiv:0909.2736v1  [astro-ph.CO]  15 Sep 2009**FULL TITLE**ASP Conference Series, Vol. **VOLUME**, **YEAR OF PUBLICATION****NAMES OF EDITORS**Setting the normalcy level of HI properties in isolatedgalaxiesD. Espada1,2, L. Verdes-Montenegro1, E. Athanassoula3, A. Bosma3, W.K. Huchtmeier4, S. Leon5, U. Lisenfeld6, J. Sabater1, J. Sulentic1, S.Verley6 and M. Yun71 Instituto de Astrof´ısica de Andaluc´ıa (IAA-CSIC) (daniel@iaa.es); 2Harvard-Smithsonian Center for Astrophysics (CfA); 3 Laboratoired’Astrophysique de Marseille; 4 Max-Planck-Institut fuerRadioastronomie (MPIfR); 5 Instituto de Radioastronomı´a Milime´trica(IRAM); 6 Universidad de Granada; 7 UMass-AmherstAbstract. Studying the atomic gas (HI) properties of the most isolatedgalaxies is essential to quantify the effect that the environment exerts on thissensitive component of the interstellar medium. We observed and compiled HIdata for a well defined sample of ∼ 800 galaxies in the Catalog of Isolated Galax-ies, as part of the AMIGA project (Analysis of the ISM in Isolated GAlaxies,http://amiga.iaa.es), which enlarges considerably previous samples used toquantify the HI deficiency in galaxies located in denser environments. By study-ing the shape of 182 HI profiles, we revisited the usually accepted result that,independently of the environment, more than half of the galaxies present a per-turbed HI disk. In isolated galaxies this would certainly be a striking result ifthese are supposed to be the most relaxed systems, and has implications in therelaxation time scales of HI disks and the nature of the most frequent perturb-ing mechanisms in galaxies. Our sample likely exhibits the lowest HI asymmetrylevel in the local Universe. We found that field samples present an excess of ∼20% more asymmetric HI profiles than that in CIG. Still a small percentageof galaxies in our sample present large asymmetries. Follow-up high resolutionVLA maps give insight into the origin of such asymmetries.1. IntroductionAtomic gas (HI) is presumably the most extended cold component of the in-terstellar medium (ISM) and is very sensitive to any kind of perturbation. Forinstance, the HI component in spiral galaxies has long been known to show bothgeometric and kinematic asymmetries (e.g. Beale & Davies 1969; Baldwin et al.1980), and the HI content is found to be deficient in galaxies in denser environ-ments (e.g. Davies & Lewis 1973). Although asymmetries have also been seenin stellar disks (e.g. Zaritsky & Rix 1997), the fact that HI is usually twice moreextended than the optical component makes it arguably a better tracer of inter-action. The study of HI global velocity profiles of galaxies has proven to be veryuseful for both the quantification of the HI content as well as the asymmetrylevel. In the context of the AMIGA project, we use HI global velocity profilesof a large sample of strictly isolated galaxies in order to: i) revise the referenceto study the HI content normalcy level in galaxies, ii) quantify the rate of HIasymmetries, and iii) study the relevance of different mechanisms producingasymmetries in galaxies, with the additional help of aperture synthesis maps.122. HI contentWe present HI data for N = 834 CIG galaxies (Catalog of Isolated Galaxies,Karachentseva 1973) and study the correlations between the HI content anddifferent parameters associated with the stellar component: optical luminosi-ties (see Figure 1, left), diameters and morphological type. We calculated HIfluxes, mean velocities, line-widths and HI masses for galaxies we observed atthe Arecibo, Effelsberg, Nanc¸ay and Green Bank (GBT) radio-telescopes, orcompiled from different sources in the literature (Espada et al. 2009). Survivalanalysis was applied in order to use the information given by upper limits. Thissample is about 3 times larger than that of Haynes & Giovanelli (1984), theprevalent reference of HI data for isolated galaxies to date, increasing consider-ably the population per morphological bin. This is important especially for theless populated bins, such as E and Sd/Irr, where our sample has a factor 5–10more galaxies. Our improved sample is thus essential as a control sample forstudies involving galaxies in denser environments. We note that to compare theHI content of two different samples, one needs to homogeneously adopt the sameconstants and corrections, since otherwise the differences may be comparable tothe observed levels of deficiency.3. Global measure of HI asymmetryThe frequency and amplitude of gaseous disk asymmetries have been studied byseveral authors, with the main conclusion that at least half of the galaxies areasymmetric even in the field (e.g. Richter & Sancisi 1994). We restricted ourstudy to a subsample of N = 182 galaxies for which we have global HI velocityprofiles with S/N > 10 and minimized undesired artificial lopsidedness. Wecalculated a flux ratio asymmetry parameter to quantify the asymmetry of theprofiles, defined as Aflux ratio = Al/h, if Al/h > 1, and 1/Al/h otherwise, whereAl/h is the ratio of the areas under the profile at velocities lower and higherthan the central velocity (e.g. Haynes et al. 1998). We minimized artificialasymmetries by avoiding large pointing offsets and poor determinations of thecentral velocity which resulted in possible errors of Aflux ratio larger than 10%.The resulting Aflux ratio distribution was characterized by a half-Gaussianprofile with a FWHM/2 of 0.13 (Figure 1, right). This width is very likelysmaller than 0.13, since remaining systematic errors were estimated to be ∼7%, mostly produced by pointing offsets and an inaccurate determination of themean velocity. For large values of the parameters, Aflux ratio > 1.3, we found atotal of 16 galaxies. This corresponds to an excess of 12 more than what wouldcorrespond to the fitted half-Gaussian profile, or a 6% of the subsample. Thisis very likely a residual of interacting systems.Among our sample of isolated galaxies we find a weak trend for largerHI asymmetries to be related to less isolated systems. We plot in Figure 2(left) the comparison of the distribution of the tidal strength (QKar) and galaxysurface number density (ηK) parameters (Verley et al. 2007a,b) for the mostsymmetric (Aflux ratio < 1.13) and the most asymmetric profiles (Aflux ratio >1.13). Smaller ηK and QKar are found for galaxies with symmetric HI profiles.In Figure 2 (right) we show the Aflux ratio cumulative probability distribu-tion of previous samples of field/isolated galaxies and compare it with that in38.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0Lb7.58.08.59.09.510.010.511.011.512.0MHIdetectionupper limitsmarginalHG84 fitAMIGA fit, only detAMIGA fit, survivalFigure 1. (Left) : MHI vs LB plot for the whole sample ofN = 837 galaxies.Detections (cross signs) as well as upper limits (arrow signs) are included. Thefit presented by Haynes & Giovanelli (1984) is shown as a red line, and thatof our sample in blue. (Right) : Aflux ratio distribution, half-Gaussian fit andthe residuals.our sample. We found a ∼ 20% excess of asymmetric profiles in samples of fieldgalaxies or not obviously interacting galaxies. The only similar distribution toours is that of Haynes et al. (1998), whose sample comprises some isolated galax-ies, although not members of CIG. The rate of asymmetric profiles is expectedto be even higher in strongly interacting galaxies.4. Origin of HI asymmetriesWe carried out a follow-up study of the origin of the HI asymmetries for eightgalaxies with the most asymmetric profiles as well as four galaxies with themost symmetric HI profiles for comparison, using VLA aperture synthesis HIobservations. One of the isolated galaxies with an asymmetric profile in thissubsample is CIG 96 (NGC 864), whose HI synthesis imaging from the VLA hasbeen studied in detail in Espada et al. (2005). The asymmetry in its HI profileis associated with a strong kinematical perturbation in the gaseous envelopeof the galaxy, where on one side the decay of the rotation curve is faster thanKeplerian. Although a companion is detected, no tidal tail is found, and it isprobably not massive enough to cause such a perturbation. Probably we arewitnessing the capture of a gaseous companion. Aperture synthesis maps forthe rest of the sources showed more symmetric structures, both in geometry andkinematics. Neither tidal tails nor relevant HI rich companions were found closeto any of the galaxies. The asymmetry was usually found in the kinematics, inthe sense that the rotation curve on one side of the galaxy was steeper. Theseresults are similar to that in other galaxies (Swaters et al. 1999), not necessarilyisolated. Given that in average galaxies in our sample did not likely undergoa major interaction since less than 3 Gyr ago (Verdes-Montenegro et al. 2005),4Figure 2. (Left) : Isolation parameter distribution (QKar and ηK) for sym-metric (Aflux ratio < 1.13, solid-line histogram) and asymmetric (Aflux ratio> 1.13, dashed-line histogram) HI profiles. The mean, standard deviationand median are shown as circle, bar and triangle signs, respectively. (Right) :Comparison of the cumulative Aflux ratio distribution between our sample(solid line) and other samples (dashed line).these asymmetries may either be the remnants of a major interaction longer ago,or of a more recent short-lived mechanism such as a minor merger.Acknowledgments. This work has been partially supported by SpanishDGI grant AYA2008-06181-C02, as well as Junta de Andalucia (Spain) grantsP08-FQM-4205-PEX and TIC-114 16-C02-01. DE is supported by the MarieCurie International fellowship MOIF-CT-2006-40298.ReferencesBaldwin, J. E., Lynden-Bell, D., & Sancisi, R. 1980, MNRAS, 193, 313Beale, J. S., & Davies, R. D. 1969, Nat, 221, 531Zaritsky, D., & Rix, H.-W. 1997, ApJ, 477, 118Bournaud, F., Combes, F., Jog, C. J., & Puerari, I. 2005, A&A, 438, 507Davies, R. D., & Lewis, B. M. 1973, MNRAS, 165, 231Espada, D., Bosma, A., Verdes-Montenegro, L., Athanassoula, E., Leon, S., Sulentic,J., & Yun, M. S. 2005, A&A, 442, 455—. 2009, in prep.Haynes, M. P., & Giovanelli, R. 1984, AJ, 89, 758Haynes, M. P., van Zee, L., Hogg, D. E., Roberts, M. S., & Maddalena, R. J. 1998, AJ,115, 62Karachentseva, V. E. 1973, Astrofizicheskie Issledovaniia Izvestiya Spetsial’noj As-trofizicheskoj Observatorii, 8, 3Matthews, L. D., van Driel, W., & Gallagher, III, J. S. 1998, AJ, 116, 1169Richter, O.-G., & Sancisi, R. 1994, A&A, 290, L9Swaters, R. A., Schoenmakers, R. H. M., Sancisi, R., & van Albada, T. S. 1999, MNRAS,304, 330Verdes-Montenegro, L., Sulentic, J., Lisenfeld, U., Leon, S., Espada, D., Garcia, E.,Sabater, J., & Verley, S. 2005, A&A, 436, 443Verley, S., et al. 2007a, A&A, 470, 505Verley, S., et al. 2007b, A&A, 472, 121

Setting the Normalcy Level of HI Properties in Isolated Galaxies

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Setting the normalcy level of HI properties in isolated galaxies

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