Leonel Gutiérrez

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.

Destruction of the Environment of the BN-KL Nebula

Resumen en: We present the velocity structure of the 2.12 micron H2 emission in Orion, obtained with an IR Fabry-Perot interferometer with a spectral resolution of 2...

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. Aims. 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. Methods. 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⊙). Results. In the dwarf regime (8.5 < log  (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). Conclusions. 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 log   (M∗/M⊙) > 9.0 per Gyr.

A STRONG DICHOTOMY IN S0 DISK PROFILES BETWEEN THE VIRGO CLUSTER AND THE FIELD

We report evidence for a striking difference between S0 galaxies in the local field and the Virgo Cluster. While field S0 galaxies have disks whose surface-brightness profiles are roughly equally divided between the three main types (Types I, II, and III: single-exponential, truncated, and antitruncated), Virgo S0s appear to be entirely lacking in disk truncations. More specifically, the fraction of truncations in S0 galaxies with M{sub B} < -17 is 28{sup +7}{sub -6}% for the field versus 0{sup +4}{sub -0}% for the Virgo Cluster galaxies; the difference is significant at the 99.7% level. The discrepancy is made up almost entirely by Type I profiles, which are almost twice as frequent in the Virgo Cluster as they are in the field. This suggests that S0 formation may be driven by different processes in cluster and field environments, and that outer-disk effects can be useful tests of S0 formation models.

PROPERTIES OF THE H II REGION POPULATIONS OF M51 AND NGC 4449 FROM Hα IMAGES WITH THE ADVANCED CAMERA FOR SURVEYS ON THE HUBBLE SPACE TELESCOPE

We have used the images from the ACS on HST in Hα, and in the neighboring continuum, to produce flux calibrated images of the large spiral galaxy M51, and the dwarf irregular NGC 4449. From these images we have derived the absolute luminosities in Hα, the areas, and the positions with respect to the galactic centers as reference points, of over 2600 Hii regions in M51 and over 270 Hii regions in NGC 4449. Using this database we have derived luminosity (L)–volume (V) relations for the regions in the two galaxies, showing that within the error limits these obey the equation L ∼ V , which differs from the linear relation expected for regions of constant uniform electron density. We discuss briefly possible models which would give rise to this behavior, notably models with strong density inhomogeneities within the regions. Plotting the luminosity functions for the two galaxies we find a break in the slope for M51 at log(L) = 38.5 dex (units in erg s) for M51 in good agreement with the previous ground-based study by Rand, and above this luminosity NGC 4449 also shows a sharp decline in its luminosity function, although the number of regions is too small to plot the function well at higher luminosities. The cumulative diameter distribution for the Hii regions of M51 shows dual behaviour, with a break at a radius close to 100 pc, the radius of regions with the break luminosity. Here too we indicate the possible physical implications. Subject headings: ISM: general — Hii regions — galaxies: structure)

The Galaxy-wide Distributions of Mean Electron Density in the H II Regions of M51 and NGC 4449

Using Advanced Camera for Surveys-Hubble Space Telescope images to yield continuum-subtracted photometric maps in H? of the Sbc galaxy M51 and the dwarf irregular galaxy NGC 4449, we produced extensive (over 2000 regions for M51 and over 200 regions for NGC 4449) catalogs of parameters of their H II regions: their H? luminosities, equivalent radii, and coordinates with respect to the galaxy centers. From these data we derived, for each region, its mean luminosity-weighted electron density, ne , determined from the H? luminosity and the radius, R, of the region. Plotting these densities against the radii of the regions, we find excellent fits for ne varying as R ?1/2. This relatively simple relation has not, as far as we know, been predicted from models of H II region structure, and should be useful in constraining future models. Plotting the densities against the galactocentric radii, r, of the regions, we find good exponential fits with scale lengths of close to 10 kpc for both galaxies. These values are comparable to the scale lengths of the H I column densities for both galaxies, although their optical structures, related to their stellar components, are very different. This result indicates that to a first approximation the H II regions can be considered in pressure equilibrium with their surroundings. We also plot the electron density of the H II regions across the spiral arms of M51, showing an envelope which peaks along the ridgelines of the arms.

An improved method for statistical studies of the internal kinematics of H II regions: the case of M83

The understanding of the formation and evolution of galaxies will not be complete until we understand the physical processes that trigger and regulate starformation in them. This work is about star formation on several size scales. It includes the kinematic study of 157 H II regions in the spiral galaxy M83, in order to test the relation, if any, between luminosity (L) and velocity dispersion(s), indicative of virialization. We found that there is no strong correlation between the mentioned variables, but only an upper envelope with a maximum luminosity for a given velocity dispersion. We demonstrated that this envelope has a slope that is strongly dependent on an accurate correction of instrumental broadening. Using our experience in H II regions, we moved to star formation at larger scales. Thus, the bulk of this thesis is on starburst galaxies and their evolutionary descendants, the postburst galaxies. A starburst is a galaxy that is suddenly creating large amounts of stars, at a rate that is not sustainable for long periods.We performed a kinematic study of a sample of 11 such objects, showing that they are, in general, not supported by rotation and that many of them are consistent with a recent merger which affected their morphology and kinematics.Furthermore, from Sloan Digital Sky Survey (SDSS) we extracted a robust sample of 1006 starbursts and 240 postbursts at redshift 0.010<z<0.083. We performed a comparative study of their structural parameters, such as effective radius, sersic index, asymmetry and absolute magnitude. We have found that the majority of starbursts and postbursts in the nearby Universe are disky galaxies, with a tendency for starbursts to have shorter effective radii and larger asymmetries.

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.

Automation of the OAN/SPM 1.5-meter Johnson telescope for operations with RATIR

The Reionization And Transients Infra-Red (RATIR) camera is intended for robotic operation on the 1.5-meter Harold Johnson telescope of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. This paper describes the work we have carried out to successfully automate the telescope and prepare it for RATIR. One novelty is our use of real-time absolute astrometry from the finder telescopes to point and guide the main telescope.

CAMILA: Infrared Camera/Spectrograph for OAN-SPM

The development of the IR camera and spectrograph (CAMILA) is described. It is based on a NICMOS 3 HgCdTe detector developed by Rockwell with a spectral response of 1 to 2.5 micrometers . The initial configuration of the system was recently concluded and consists of the following components: detector cryostat, detector control electronics, low noise preamplifiers, detector-PC interface, operating system and optics. The characterization of the electronics and the science grade chip are presented. The complete optical configuration allows the following modes of operation: direct imaging (12 filter positions), polarimetry and spectroscopy on three dispersion modes (low, medium, and high resolution). Preliminary spectroscopic results at the H band with R equals 1500 are presented. The project is a collaborative effort of groups from IAUNAM and UMASS (Amherst) and will be used mainly at the 2.1-m telescope of San Pedro Martir, B.C. (Mexico).