Martha P. Haynes

Hα3: an Hα imaging survey of HI selected galaxies from ALFALFA - VI. The role of bars in quenching star formation from z = 3 to the present epoch

A growing body of evidence indicates that the star formation rate per unit stellar mass (sSFR) decreases with increasing mass in normal main-sequence star-forming galaxies. Many process es have been advocated as being responsible for this trend (a lso known as mass quenching), e.g., feedback from active galactic nuc lei (AGNs), and the formation of classical bulges. In order t o improve our insight into the mechanisms regulating the star formati on in normal star-forming galaxies across cosmic epochs, we det rmine a refined star formation versus stellar mass relation in the l ocal Universe. To this end we use the H α narrow-band imaging followup survey (Hα3) of field galaxies selected from the HI Arecibo Legacy Fast A LF Survey (ALFALFA) in the Coma and Local superclusters. By complementing this local determination with high-redshift measurements from the literature, we re construct the star formation history of main-sequence galaxies as a funct ion of stellar mass from the present epoch up to z = 3. In agreement with previous studies, our analysis shows that quenching mechan isms occur above a threshold stellar mass Mknee that evolves with redshift as∝ (1 + z)2. Moreover, visual morphological classification of individ ual objects in our local sample reveals a sharp increase in th e fraction of visually classified strong bars with mass, hinti ng that strong bars may contribute to the observed downturn i n the sSFR aboveMknee. We test this hypothesis using a simple but physically motiv ated numerical model for bar formation, finding that strong bars can rapidly quench star formation in the central few kpc of field galaxies. We conclude that strong bars contribute si gnificantly to the red colors observed in the inner parts of massive galax ies, although additional mechanisms are likely required to quench the star formation in the outer regions of massive spiral galaxi es. Intriguingly, when we extrapolate our model to higher re dshifts, we successfully recover the observed redshift evolution for Mknee.A growing body of evidence indicates that the star formation rate per unit stellar mass (sSFR) decreases with increasing mass in normal main-sequence star-forming galaxies. Many processes have been advocated as being responsible for this trend (also known as mass quenching), e.g., feedback from active galactic nuclei (AGNs), and the formation of classical bulges. In order to improve our insight into the mechanisms regulating the star formation in normal star-forming galaxies across cosmic epochs, we determine a refined star formation versus stellar mass relation in the local Universe. To this end we use the Hα narrow-band imaging followup survey (Hα3) of field galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) in the Coma and Local superclusters. By complementing this local determination with high-redshift measurements from the literature, we reconstruct the star formation history of main-sequence galaxies as a function of stellar mass from the present epoch up to z = 3. In agreement with previous studies, our analysis shows that quenching mechanisms occur above a threshold stellar mass Mknee that evolves with redshift as ∝(1 + z) 2 . Moreover, visual morphological classification of individual objects in our local sample reveals a sharp increase in the fraction of visually classified strong bars with mass, hinting that strong bars may contribute to the observed downturn in the sSFR above Mknee. We test this hypothesis using a simple but physically motivated numerical model for bar formation, finding that strong bars can rapidly quench star formation in the central few kpc of field galaxies. We conclude that strong bars contribute significantly to the red colors observed in the inner parts of massive galaxies, although additional mechanisms are likely required to quench the star formation in the outer regions of massive spiral galaxies. Intriguingly, when we extrapolate our model to higher redshifts, we successfully recover the observed redshift evolution for Mknee. Our study highlights how the formation of strong bars in massive galaxies is an important mechanism in regulating the redshift evolution of the sSFR for field main-sequence galaxies.

Hα3: an Hα imaging survey of HI selected galaxies from ALFALFA - II. Star formation properties of galaxies in the Virgo cluster and surroundings

Context. We present the analysis of H alpha 3, an H alpha narrow-band imaging follow-up survey of 409 galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) in the Local Supercluster, including the Virgo cluster, in the region 11(h) textless RA textless 16(h); 4(o) textless Dec textless 16(o) 350 textless cz textless 2000 km s(-1). Aims. Taking advantage of H alpha 3, which provides the complete census of the recent massive star formation rate (SFR) in HI-rich galaxies in the local Universe and of ancillary optical data from SDSS we explore the relations between the stellar mass, the HI mass, and the current, massive SFR of nearby galaxies in the Virgo cluster. We compare these with those of isolated galaxies in the Local Supercluster, and we investigate the role of the environment in shaping the star formation properties of galaxies at the present cosmological epoch. Methods. By using the H alpha hydrogen recombination line as a tracer of recent star formation, we investigated the relationships between atomic neutral gas and newly formed stars in different environments (cluster and field), for many morphological types (spirals and dwarfs), and over a wide range of stellar masses (10(7.5) to 10(11.5) M-circle dot). To quantify the degree of environmental perturbation, we adopted an updated calibration of the HI deficiency parameter which we used to divide the sample into three classes: unperturbed galaxies (Def(HI) textless= 0.3), perturbed galaxies (0.3 textless Def(HI) textless 0.9), and highly perturbed galaxies (Def(HI) textgreater= 0.9). Results. Studying the mean properties of late-type galaxies in the Local Supercluster, we find that galaxies in increasing dense local galaxy conditions (or decreasing projected angular separation from M 87) show a significant decrease in the HI content and in the mean specific SFR, along with a progressive reddening of their stellar populations. The gradual quenching of the star formation occurs outside-in, consistently with the predictions of the ram pressure model. Once considered as a whole, the Virgo cluster is effective in removing neutral hydrogen from galaxies, and this perturbation is strong enough to appreciably reduce the SFR of its entire galaxy population. Conclusions. An estimate of the present infall rate of 300-400 galaxies per Gyr in the Virgo cluster is obtained from the number of existing HI-rich late-type systems, assuming 200-300 Myr as the time scale for HI ablation. If the infall process has been acting at a constant rate, this would imply that the Virgo cluster has formed approximately 2 Gyr ago, consistently with the idea that Virgo is in a young state of dynamical evolution.

Hα3: an Hα imaging survey of HI selected galaxies from ALFALFA - III. Nurture builds up the Hubble sequence in the Great Wall

Context. We present the analysis of Hα3, an Hα narrow-band imaging follow-up survey of galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) in the Coma supercluster. nAims. Taking advantage of Hα3, which provides the complete census of the recent star formation in HI-rich galaxies in the local universe, we explored the hypothesis that a morphological sequence of galaxies of progressively earlier type and lower gas-content exists in the neighborhood of a rich cluster of galaxies such as Coma, with a specific star formation activity that decreases with increasing local galaxy density and velocity dispersion. nMethods. By using the Hα hydrogen recombination line as a tracer of the “instantaneous” star formation, complemented with optical colors from SDSS, we investigated the relationships between atomic neutral gas and newly formed stars in different local galaxy density intervals, for many morphological types, and over a wide range of stellar masses (109 to 1011.5 M⊙). nResults. In the dwarf regime (8.5 < logu2009u2009(M∗/M⊙) < 9.5) we identify a four-step sequence of galaxies with progressively redder colors (corrected for dust extinction), i.e., of decreasing specific star formation, from (1) HI-rich late-type galaxies (LTGs) belonging to the blue cloud that exhibit extended plus nuclear star formation, (2) ~0.1 mag redder, HI-poor LTGs with nuclear star formation only, (3) ~0.35 mag redder, HI-poor galaxies without either extended or nuclear star formation, but with nuclear post-star-burst (PSB) signature, (4) ~ 0.5 mag redder early-type galaxies (ETGs) that belong to the red sequence, and show no gas or star formation on all scales. Along this sequence the quenching of the star formation proceeds radially outside-in. The progression toward redder colors found along this “morphological” (gas content) sequence is comparable to the one obtained from increasing the local galaxy density, from cosmic filaments (1 2), to the rich clusters (2 3 4). nConclusions. In the dwarf regime we find evidence for an evolution of HI-rich LTGs into ETGs through HI-poor LTGs and PSB galaxies driven by the environment. We identify ram-pressure as the mechanism most likely responsible for this transformation. We conclude that infall of galaxies has proceeded for the last 7.5 Gyr, building up the Coma cluster at a rate of approximately 100 galaxies with logu2009u2009 (M∗/M⊙) > 9.0 per Gyr.

Extragalactic Neutral Hydrogen

The 21-cm hyperfine transition of neutral hydrogen was first detected in the Milky Way in 1951 by Ewen and Purcell. Two years later (Kerr and Hindman 1953), the HI emission of the Magellanic Clouds was observed from Australia. Largely as a result of the pioneering efforts of M.S. Roberts, by the time of his comprehensive review (Roberts 1975; the reader is referred to this source for the early development of the field), HI in about 140 extragalactic objects had been detected. Since then, mostly with the Green Bank 91-m, the Nancay, the Effelsberg, and more recently the Arecibo telescopes, the line has been observed in emission in thousands of galaxies, to distances 104 times greater than that of the Magellanic Clouds, and in absorption out to redshifts greater than 2. For the first twenty years, single-dish telescopes provided the vast majority of the HI data. By the mid-seventies, the techniques of spectral line aperture synthesis, developed especially at Cambridge, Green Bank, and Owens Valley, bloomed in full maturity at Westerbork and more recently at the VLA. The contributions of single-dish instruments have, however, remained important, especially for survey-oriented projects that require high-sensitivity observations of many noncontiguous regions of sky, and for pure detection experiments.

Neutral hydrogen in isolated galaxies. II. The large angular diameter galaxies

Fifty-two of the large angular diameter (a> or =2.5) galaxies included in the 21-cm survey of isolated galaxies being undertaken at Arecibo by Haynes and Giovanelli have been mapped along their optical major axes using the 305-m telescope and the low sidelobe flat feed system. The observed fluxes have then been compared with a numerical convolution of an assumed H I distribution sigma/sub H/(r) and the beam pattern G(theta) to produce an estimate of the characteristic size. The derived H I scale length R/sub 70/ is that radius interior to which 70% of the models H I mass is contained. With still a significant scatter, the H I diameter D/sub 70/ = 2R/sub 70/ is on the average about 1.2 times the UGC blue diameter a, and shows no dependence on morphological type for types later than Sa. Application of the observed relationship between H I size and optical diameter and of an assumed double Gaussian (centrally depressed) H I surface density distribution produces proper corrections for source to beam size. Corrected fluxes derived from Arecibo data do not differ systematically from those measured at the 91-m telescope, proving the applicability of the calibration and correction procedure. The H Imorexa0» mass M/sub H/ is shown to be nearly proportional to the square of the linear H I diameter, implying that the H I surface density averaged over the disk is almost constant.«xa0less

Hα3: an Hα imaging survey of HI selected galaxies from ALFALFA - I. Catalogue in the Local Supercluster

Context. We present Hα3 (acronym for Hα − αα), an Hα narrow-band imaging survey of ∼400 galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) in the Local Supercluster, including the Virgo cluster. Aims. By using hydrogen recombination lines as a tracer of recent star formation, we aim to investigate the relationships between atomic neutral gas and newly formed stars in different environments (cluster and field), morphological types (spirals and dwarfs), and over a wide range of stellar masses (∼10 7.5 −10 11.5 M� ).

Hα3: an Hα imaging survey of HI selected galaxies from ALFALFA - IV. Structure of galaxies in the Local and Coma superclusters

Context. We present the analysis of the galaxy structural parameters from Hα3, an Hα narrow-band imaging follow-up survey of ∼800 galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) in the Local supercluster, including the Virgo cluster, and in the Coma supercluster. Aims. Taking advantage of Hα3, which provides the complete census of the recent star-forming, HI-rich galaxies in the local universe, we aim to investigate the structural parameters of the young ( 1 Gyr) stellar populations. By comparing the sizes of these stellar components, we investigated the spatial scale on which galaxies are growing at the present cosmological epoch and the role of the environment in quenching the star-formation activity. Methods. We computed the concentration, asymmetry, and clumpiness (CAS) structural parameters for recently born and old stars. To quantify the sizes we computed half-light radii and a new parameter dubbed EW/r based on the half-light radius of the Hα equivalent width map. To highlight the environmental perturbation, we adopt an updated calibration of the HI-deficiency parameter (DefHI )t hat we use to divide the sample in unperturbed galaxies (DefHI ≤ 0.3) and perturbed galaxies (DefHI > 0.3). Results. The concentration index computed in the r band depends on the stellar mass and on the Hubble type these variables are related because most massive galaxies are bulge dominated therefore highly concentrated. Going toward later spirals and irregulars the concentration index and the mass decrease along with the bulge-to-disk ratio. Blue compact dwarfs (BCDs) are an exception because they have similar mass, but they are more concentrated than dwarf irregulars. The asymmetry and the clumpiness increase along the spiral sequence up to Sc-Sd, but they decrease going in the dwarf regime, where the light distribution is smooth and more symmetric. When measured on Hα images, the CAS parameters show no obvious correlations with Hubble type. Irrespective of whether we used the ratio between effective radii or the EW/r parameter, we found that the concentration index is the main parameter that describes the current growth of isolated galaxies but, for a fixed concentration, the stellar mass plays a second-order role. At the present epoch, massive galaxies are growing inside-out, conversely, the dwarfs are growing on the scale of their already assembled mass.

Asymmetry in Isolated, Morphologically Normal Sa Galaxies

We have examined the morphological and dynamical H I symmetry properties of a sample of moderately inclined Sa galaxies classified as morphologically normal. The sample galaxies were known a priori to exhibit kinematic peculiarities ranging from warps to independent, wholly decoupled disks and are possibly the remnants of minor mergers. We compare the asymmetry of the rotation curves to global kinematic asymmetry and find a relationship between rotation curve asymmetry and the kinematic n = 2 mode. We have also examined the kinematics of these galaxies following the discussion of Briggs and find that the warps observed in the H I disks of these galaxies deviate significantly from the simple rules for warps that commonly apply.

Hα3: an Hα imaging survey of HI selected galaxies from ALFALFA - V. The Coma supercluster survey completion

Neutral hydrogen represents the major observable baryonic constituent of galaxies that fuels the formation of stars through the transformation in molecular hydrogen. The emission of the hydrogen recombination line Halpha is the most direct tracer of the process that transforms gas (fuel) into stars. We continue to present Halpha3 (acronym for Halpha-alpha-alpha), an extensive Halpha+[NII] narrow-band imaging campaign of galaxies selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA), using the instrumentation available at the San Pedro Martir observatory (Mexico). In only four years since 2011 we were able to complete in 48 nights the Halpha imaging observations of 724 galaxies in the region of the Coma supercluster 10^h < R.A. <16^h; 24^o < Dec. <28^o and 3900<cz<9000 kms^{-1}. Of these, 603 are selected from the HI Arecibo Legacy Fast ALFA Survey (ALFALFA) and constitute a 97% complete sample. They provide for the first time a complete census of the massive star formation properties of local gas-rich galaxies belonging to different environments (cluster vs filaments), morphological type (spirals vs dwarf Irr), over a wide range of stellar mass (10^{8}-10^{11.5} Modot) in the Coma Supercluster. The present Paper V provides the Halpha data and the derived star formation rates for the observed galaxies.