Noah Brosch

THE ARECIBO LEGACY FAST ALFA SURVEY. I. SCIENCE GOALS, SURVEY DESIGN, AND STRATEGY

The recently initiated Arecibo Legacy Fast ALFA (ALFALFA) survey aims to map ~7000 deg2 of the high Galactic latitude sky visible from Arecibo, providing a H I line spectral database covering the redshift range between -1600 and 18,000 km s-1 with ~5 km s-1 resolution. Exploiting Arecibos large collecting area and small beam size, ALFALFA is specifically designed to probe the faint end of the H I mass function in the local universe and will provide a census of H I in the surveyed sky area to faint flux limits, making it especially useful in synergy with wide-area surveys conducted at other wavelengths. ALFALFA will also provide the basis for studies of the dynamics of galaxies within the Local Supercluster and nearby superclusters, allow measurement of the H I diameter function, and enable a first wide-area blind search for local H I tidal features, H I absorbers at z < 0.06, and OH megamasers in the redshift range 0.16 < z < 0.25. Although completion of the survey will require some 5 years, public access to the ALFALFA data and data products will be provided in a timely manner, thus allowing its application for studies beyond those targeted by the ALFALFA collaboration. ALFALFA adopts a two-pass, minimum intrusion, drift scan observing technique that samples the same region of sky at two separate epochs to aid in the discrimination of cosmic signals from noise and terrestrial interference. Survey simulations, which take into account large-scale structure in the mass distribution and incorporate experience with the ALFA system gained from tests conducted during its commissioning phase, suggest that ALFALFA will detect on the order of 20,000 extragalactic H I line sources out to z ~ 0.06, including several hundred with H I masses M < 107.5 M⊙.

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS) - I. The UV luminosity function of the central 12 sq. deg

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS) is a complete blind survey of the Virgo cluster covering similar to 40 sq. deg in the far UV (FUV, lambda(eff) = 1539 angstrom, Delta lambda = 442 angstrom) and similar to 120 sq. deg in the near UV (NUV, lambda(eff) = 2316 angstrom, Delta lambda = 1060 angstrom). The goal of the survey is to study the ultraviolet (UV) properties of galaxies in a rich cluster environment, spanning a wide luminosity range from giants to dwarfs, and regardless of prior knowledge of their star formation activity. The UV data will be combined with those in other bands (optical: NGVS; far-infrared - submm: HeViCS; HI: ALFALFA) and with our multizone chemo-spectrophotometric models of galaxy evolution to make a complete and exhaustive study of the effects of the environment on the evolution of galaxies in high density regions. We present here the scientific objectives of the survey, describing the observing strategy and briefly discussing different data reduction techniques. Using UV data already in-hand for the central 12 sq. deg we determine the FUV and NUV luminosity functions of the Virgo cluster core for all cluster members and separately for early-and late-type galaxies and compare it to the one obtained in the field and other nearby clusters (Coma, A1367). This analysis shows that the FUV and NUV luminosity functions of the core of the Virgo clusters are flatter (alpha similar to -1.1) than those determined in Coma and A1367. We discuss the possible origin of this difference.

High-rate active galaxy monitoring at the wise observatory. III, The broad-line region of NGC 4151

Results of an AGN monitoring program for the Seyfert galaxy NGC 4151 are presented. The space and velocity distribution of the broad large region (BLR) gas in this AGN are analyzed. Through cross-correlation, it is found that both Hα and Hβ lag the continuum variations by 9 ± 12 days. Through Fourier and maximun entropy deconvolutions of the continuum and emission-line curves, the approximate transfert function of the BLR in this object is recovered.

THE ARECIBO LEGACY FAST ALFA SURVEY. II. RESULTS OF PRECURSOR OBSERVATIONS

In preparation for the full Arecibo Legacy Fast ALFA (ALFALFA) extragalactic H I survey, precursor observations were carried out in 2004 August–September with the seven-beam Arecibo L-band Feed Array (ALFA) receiver system and the Wideband Arecibo Pulsar Processor spectral processors. While these observations were geared mainly at testing and debugging survey strategy, hardware, and software, approximately 48 hr of telescope time yielded science-quality data. The efficiency of system usage (allowing for minor malfunctions and the impact of radio-frequency interference) during that time was 75%. From those observations, an initial list of 730 tentative detections of varying degrees of reliability was extracted. Ninety-eight high signal-to-noise ratio candidates were deemed to be bona fide H I line detections. To test our ability to discriminate cosmic signals from radio-frequency interference and noise, 165 candidates ranging in reliability likelihood were reobserved with the single-beam L-band wide system at Arecibo in 2005 January–February. Of those, 41% were confirmed as real. We present the results of both the ALFA and the single-beam observations for the sample of 166 confirmed H I sources, as well as our assessment of their optical counterparts. Of the 166 sources, 62 coincided with previously known H I sources, while optical redshifts were available for an additional 18 galaxies; thus, 52% of the redshifts reported here were previously unknown. Of the 166 H I detections, 115 are identified with previously cataloged galaxies of either known or unknown redshift, leaving 51 objects identified for the first time. Because of the higher sensitivity of the Arecibo system, fewer than 10% of the 166 H I sources would have been detected by a HIPASS-like survey of the same region. Three of the objects have H I masses less than 107 M⊙. The full ALFALFA survey, which commenced in 2005 February, should detect more than 100 times as many objects of similarly low H I mass over the next 5 years.

The Arecibo Galaxy Environment Survey: precursor observations of the NGC 628 group

The Arecibo Galaxy Environment Survey (AGES) is one of several HI surveys utilising the new Arecibo L-band Feed Array (ALFA) fitted to the 305m radio telescope at Arecibo. The survey is specifically designed to investigate various galactic environments to higher sensitivity, higher velocity resolution and higher spatial resolution than previous fully sampled, 21 cm multibeam surveys. The emphasis is on making detailed observations of nearby objects although the large system bandwidth (100 MHz) will allow us to quantify the HI properties over a large instantaneous velocity range. In this paper we describe the survey and its goals and present the results from the precursor observations of a 5 degree x 1 degree region containing the nearby (~10 Mpc) NGC 628 group. We have detected all the group galaxies in the region including the low mass (M{HI}~10^7Mo) dwarf, dw0137+1541 (Briggs, 1986). The fluxes and velocities for these galaxies compare well with previously published data. There is no intra-group neutral gas detected down to a limiting column density of 2x10^{18}cm^{-2}. In addition to the group galaxies we have detected 22 galaxies beyond the NGC 628 group, 9 of which are previously uncatalogued.(Abridged)

HI content and other structural properties of galaxies in the Virgo cluster from the Arecibo Legacy Fast ALFA Survey

We report the results of an HI blind survey of 80deg^2 of the Virgo cluster, based on the 08deg 10^7.5-8 M_sun; vi) less than 1% of early-type galaxies contain neutral hydrogen with M_HI>10^7.5-8 M_sun (di Serego Alighieri et al. 2007).

Studies of galaxies in voids I. H i observations of Blue Compact Galaxies

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 Vhel 11 000 km s 1 , two BCGs in the void behind the Virgo cluster and 11 BCGs in denser environments. H i fluxes and prole widths, as well as estimates of total H i 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 eld 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(H i)/LB. We nd that for the same blue luminosity, for MB > 18: m 0, BCGs in lower density environment have on average more H i .T he slope of the M(H i)/LB L 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 = 0.4 for voids.

Are interactions the primary triggers of star formation in dwarf galaxies

We investigate the assumption that the trigger of star formation in dwarf galaxies is interactions with other galaxies, in the context of a search for a ‘primary’ trigger of a first generation of stars. This is cosmologically relevant because the galaxy formation process consists not only of the accumulation of gas in a gravitational potential well but also of the triggering of star formation in this gas mass, and also because some high-z potentially primeval galaxy blocks look like nearby star-forming dwarf galaxies. We review theoretical ideas proposed to account for the tidal interaction triggering mechanism and present a series of observational tests of this assumption using published data. We also show results of a search in the vicinity of a composite sample of 96 dwarf late-type galaxies for interaction candidates showing star formation. The small number of possible perturbing galaxies identified in the neighbourhood of our sample galaxies, along with similar findings from other studies, supports the view that tidal interactions may not be relevant as primary triggers of star formation. We conclude that interactions between galaxies may explain some forms of star formation triggering, perhaps in central regions of large galaxies, but they do not seem to be significant for dwarf galaxies and, by inference, for first-time galaxies forming at high redshifts. Intuitive reasoning, based on an analogy with stellar dynamics, shows that conditions for primary star formation triggering may occur in gas masses oscillating in a dark-matter gravitational potential. We propose this mechanism as a plausible primary trigger scenario, which would be worth investigating theoretically.

High-rate spectroscopic active galactic nucleus monitoring at the Wise Observatory. I. Markarian 279

Spectrophotometric monitoring of a sample of AGNs has achieved a temporal sampling rate of once every 3-4 days, over a period of 5-7 months. By observing each object simultaneously with a nearby field star, in a long-slit spectroscopy mode, accurate flux measurements were obtained even during bad weather and full moon. Results for the Seyfert 1 galaxy MrK 279 are discussed. This object brightened by 20-50 percent in H-alpha, H-beta, and the optical continuum during the period of observation. The high sampling rate and small error allow the determination, through cross-correlation, of the lag in the emission-line response to the continuum brightening. A lag of 12 days is observed. The size of the broadline region (BLR) is estimated to be 12 + or - 3 light days in this object; the results rule out, at the 95 percent significance level, a BLR of 21 light-days or larger. This result is in conflict with the standard photoionization model of AGNs, which predicts a BLR size larger by an order of magnitude. 27 refs.

High-rate spectroscopic active galactic nucleus monitoring at the wise observatory. II: NGC 5548

Les observations spectroscopiques de la galaxie de Seyfert de type 1, NGC 5548, sont analysees. Les fonctions de correlation croisee entre le continuum et les raies Hα et Hβ sont etudiees. La taille de la region de raies larges est determinee