THE ARECIBO LEGACY FAST ALFA SURVEY. V. THE H I SOURCE CATALOG OF THE ANTI-VIRGO REGION AT δ = +27° (original) (raw)
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Searching for Dwarf HαEmission-line Galaxies within Voids. III. First Spectra
The Astrophysical Journal, 2017
The presence or absence of dwarf galaxies with >-¢ M 14 r in low-density voids is determined by the nature of dark matter halos. To better understand what this nature is, we are conducting an imaging survey through redshifted Hα filters to look for emission-line dwarf galaxies in the centers of two nearby galaxy voids called FN2 and FN8. Either finding such dwarfs or establishing that they are not present is a significant result. As an important step in establishing the robustness of the search technique, we have observed six candidates from the survey of FN8 with the Gillett Gemini telescope and GMOS spectrometer. All of these candidates had emission, although none was Hα. The emission in two objects was the [O III]λ4959, 5007 doublet plus Hβ, and the emission in the remaining four was the [O II]λ3727 doublet, all from objects beyond the void. While no objects were within the void, these spectra show that the survey is capable of finding emission-line dwarfs in the void centers that are as faint as~-¢ M 12.4 r , should they be present. These spectra also show that redshifts estimated from our filtered images are accurate to several hundred km s −1 if the line is identified correctly, encouraging further work in finding ways to conduct redshift surveys through imaging alone.
Studies of galaxies in voids. I. HI observations of Blue Compact Galaxies
Astronomy & Astrophysics, 2002
We present here results of studies of the properties of galaxies located in very low density environments. We observed 26 blue compact galaxies (BCGs) from the Second Byurakan (SBS) and Case surveys located in voids with the radial velocities V < 11000 km/s, two BCGs in the void behind the Virgo cluster and 11 BCGs in denser environments. HI fluxes and profile widths, as well as estimates of total HI masses, are presented for the 27 detected galaxies (of which 6 are in three galaxy pairs and are not resolved by the radiotelescope beam). Preliminary comparisons of void BCGs with similar objects from intermediate density regions - in the general field and the Local Supercluster (sub-samples of BCGs in the SBS zone) and in the dense environment of the Virgo Cluster (a BCD sample) - are performed using the hydrogen-to-blue-luminosity ratio M(HI)/L_B. We find that for the same blue luminosity, for M_B > -18.0, BCGs in lower density environment have on average more HI. The slope (beta) of the M(HI)/L_B proportional to L^(beta) for BCGs shows a trend of steepening with decreasing bright galaxy density, being very close to zero for the densest environment considered here and reaching (beta) = -0.4 for voids.
Monthly Notices of the Royal Astronomical Society
We measure the H I mass function (HIMF) and velocity width function (WF) across environments over a range of masses, 7.2 < log M H I /M < 10.8, and profile widths, 1.3 log (km s −1 ) < log (W) < 2.9 log (km s −1 ), using a catalogue of ∼7300 H I-selected galaxies from the Arecibo Legacy Fast ALFA (ALFALFA) Survey, located in the region of sky where ALFALFA and Sloan Digital Sky Survey (Data Release 7) North overlap. We divide our galaxy sample into those that reside in large-scale voids (void galaxies) and those that live in denser regions (wall galaxies). We find the void HIMF to be well fitted by a Schechter function with normalization * = (1.37 ± 0.1) × 10 −2 y h 3 Mpc −3 , characteristic mass log(M * H I /M ) + 2 log h 70 = 9.86 ± 0.02, and low-mass-end slope α = −1.29 ± 0.02. Similarly, for wall galaxies, we find best-fitting parameters * = (1.82 ± 0.03) × 10 −2 h 3 Mpc −3 , log(M * H I /M ) + 2 log h 70 = 10.00 ± 0.01, and α = −1.35 ± 0.01. We conclude that void galaxies typically have slightly lower H I masses than their non-void counterparts, which is in agreement with the dark matter (DM) halo mass function shift in voids assuming a simple relationship between DM mass and H I mass. We also find that the low-mass slope of the void HIMF is similar to that of the wall HIMF suggesting that there is either no excess of low-mass galaxies in voids or there is an abundance of intermediate H I mass galaxies. We fit a modified Schechter function to the ALFALFA void WF and determine its best-fitting parameters to be * = 0.21 ± 0.1 h 3 Mpc −3 , log (W * ) = 2.13 ± 0.3, α = 0.52 ± 0.5, and high-width slope β = 1.3 ± 0.4. For wall galaxies, the WF parameters are * = 0.022 ± 0.009 h 3 Mpc −3 , log (W * ) = 2.62 ± 0.5, α = −0.64 ± 0.2, and β = 3.58 ± 1.5. Because of large uncertainties on the void and wall WFs, we cannot conclude whether the WF is dependent on the environment.
Nearby void dwarf galaxies: recent results, the ongoing project and prospects
Proceedings of the International Astronomical Union
Properties of dwarf galaxies formed and evolved in the lowest density environment remain largely unexplored and poorly understood. Especially this concerns the low-mass end (Mbar < 109M⊙). We overview the results of systematic study of a hundred void dwarfs from the nearby Lynx-Cancer void. We describe the ongoing project aiming to form Nearby Void galaxy sample (R < 25 Mpc) over the whole sky. 1354 objects with distances less than 25 Mpc fall within 25 voids delineated by 460 luminous galaxies/groups. The void major sizes range from 13 to 37 Mpc. 1088 of 1354 void galaxies reside deeply in voids, having distances to the nearest luminous neighbour of 2–11 Mpc. 195 nearest void galaxies reside in the Local Volume. We summarize the main statistical properties of the new sample and outline the prospects of study of both, the void dwarf properties and the fine structure of voids.
Galaxy And Mass Assembly (GAMA): the bright void galaxy population in the optical and mid-IR
Monthly Notices of the Royal Astronomical Society, 2015
We examine the properties of galaxies in the Galaxies and Mass Assembly (GAMA) survey located in voids with radii >10 h −1 Mpc. Utilizing the GAMA equatorial survey, 592 void galaxies are identified out to z ≈ 0.1 brighter than M r = −18.4, our magnitude completeness limit. Using the W Hα versus [N II]/Hα (WHAN) line strength diagnostic diagram, we classify their spectra as star forming, AGN, or dominated by old stellar populations. For objects more massive than 5 × 10 9 M , we identify a sample of 26 void galaxies with old stellar populations classed as passive and retired galaxies in the WHAN diagnostic diagram, else they lack any emission lines in their spectra. When matched to Wide-field Infrared Survey Explorer mid-IR photometry, these passive and retired galaxies exhibit a range of mid-IR colour, with a number of void galaxies exhibiting [4.6] − [12] colours inconsistent with completely quenched stellar populations, with a similar spread in colour seen for a randomly drawn non-void comparison sample. We hypothesize that a number of these galaxies host obscured star formation, else they are star forming outside of their central regions targeted for single-fibre spectroscopy. When matched to a randomly drawn sample of non-void galaxies, the void and non-void galaxies exhibit similar properties in terms of optical and mid-IR colour, morphology, and star formation activity, suggesting comparable mass assembly and quenching histories. A trend in mid-IR [4.6] − [12] colour is seen, such that both void and non-void galaxies with quenched/passive colours <1.5 typically have masses higher than 10 10 M , where internally driven processes play an increasingly important role in galaxy evolution.
Intergalactic Hydrogen Clouds OT Low Redshift: Connections to Voids and Dwarf Galaxies
The Astronomical Journal, 1996
We provide new post-COSTAR data on one sightline (Mrk 421) and updated data from another (I Zw 1) from our Hubble Space Telescope (HST) survey of intergalactic Lyα clouds located along sightlines to four bright quasars passing through well-mapped galaxy voids (16,000 km s −1 pathlength) and superclusters (18,000 km s −1). We report two more definite detections of low-redshift Lyα clouds in voids: one at 3047 km s −1 (heliocentric) toward Mrk 421 and a second just beyond the Local Supercluster at 2861 km s −1 toward I Zw 1, confirming our earlier discovery of Lyα absorption clouds in voids (Stocke et al. 1995). We have now identified 10 definite and 1 probable low-redshift neutral hydrogen absorption clouds toward four targets, a frequency of approximately one absorber every 3400 km s −1 above 10 12.7 cm −2 column density. Of these 10 absorption systems, 3 lie within voids; the probable absorber also lies in a void. Thus, the tendency of Lyα absorbers to "avoid the voids" is not as clear as we found previously. If the Lyα clouds are approximated as homogeneous spheres of 100 kpc radius, their masses are ∼ 10 9 M ⊙ (about 0.01 times that of bright L * galaxies) and they are 40 times more numerous, comparable to the density of dwarf galaxies and of low-mass halos in numerical CDM simulations. The Lyα clouds contribute a fraction Ω cl ≈ 0.003h −1 75 to the closure density of the universe, comparable to that of luminous matter. These clouds probably require a substantial amount of non-baryonic dark matter for gravitational binding. They may represent extended haloes of low-mass protogalaxies which have not experienced significant star formation or low-mass dwarf galaxies whose star formation ceased long ago, but blew out significant gaseous material. c
Local and large-scale effects on the astrophysics of void galaxies
Monthly Notices of the Royal Astronomical Society
Galaxies in cosmic voids have been reported with properties related to a delayed evolution compared to the rest of the Universe. These characteristics reflect the interaction of galaxies with the environment. However, it is not clear the degree of influence of the large-scale structure on the properties of void galaxies or if these are only influenced by the low local density around them typical of these regions. In this article, we identified cosmic voids in the SDSS-DR16 and studied the g–r colour, star formation rate, and concentration of galaxies. We identified galaxy groups to characterize the local environment and studied the properties of galaxies as a function of total and stellar masses, separately analysing those in voids and the general sample. Our results show that galaxies that inhabit haloes of a given mass (below sim1013.5rmModot{\sim}10^{13.5}{\rm M}_{\odot }sim1013.5rmModot), are bluer, have a higher star formation rate and are less concentrated when the host halo is inside voids compared to oth...
The Search for Intergalactic Hydrogen Clouds in Voids
The Astrophysical Journal, 2002
I present the results of a search for intergalactic hydrogen clouds in voids. Clouds are detected by their HI Lyα absorption lines in the HST spectra of low-redshift AGN. The parameter with which the environments of clouds are characterized is the tidal field, for this places a lower limit on the cloud massdensity which is dynamically stable against disruption. The summing of the tidal fields along these lines of sight is managed by the use of galaxy redshift catalogs. The analytical methodology employed here has been designed to detect gas clouds whose expansion following reionization is restrained by dark matter perturbations. The end-products of the analysis of data are the cloud equivalent width distribution functions (EWDF) of catalogs formed by sorting clouds according to various tidal field upper, or lower limits. Cloud EWDFs are steep in voids (d log(dN /dz)/d log(W) = S ∼ −1.5 ± 0.2), but flatter in high tidal field zones (S ∼ −0.5 ± 0.1). Most probable cloud Doppler parameters are ∼ 30 km s −1 in voids and ∼ 60 km s −1 in proximity to galaxies. In voids, the cumulative line density at low EW (W ≃ 15 mÅ) is essentially equal to that of the mean EWDF, ∼ 500 per unit redshift. The void filling factor is found to be 0.87 ≤ f v ≤ 0.94. The void EWDF is remarkably uniform over this volume with a possible tendency for more massive clouds to be in void centers. The size and nature of the void cloud population suggested by this study is completely unanticipated by the results of published 3-D simulations, which predict that most clouds are in filamentary structures around galaxy concentrations, and that very few observable absorbers would lie in voids. Strategies for modeling this population are briefly discussed.
Surveying for Dwarf Galaxies Within the Heart of the Void FN8
2016
The presence or absence of dwarf galaxies with M ′ r > −14 in low-density volumes correlates with dark matter halos and how they affect galaxy formation: some theories say dwarfs should be present while others say they should not. To help discriminate between theories, we have conducted a red-shifted Hα imaging survey for dwarf galaxies with M ′ r > −14 in the heart of the well-defined void FN8 using the KPNO 4m Mayall telescope and Mosaic Imager. These data have furnished 1187 candidates in a four square degree area. Subject headings: large scale structure of the universe, galaxies: dwarf, galaxies: luminosity function,