We have extended our H{alpha} objective prism survey of eight low-redshift clusters (viz. Abell 262, 347, 400, 426, 569, 779, 1367 and 1656) to include a complete sample of early-type galaxies within 1.5 Abell radii of the cluster centres. Of the 379 galaxies surveyed, 3 per cent of E, E-S0 galaxies, 6 per cent of S0 galaxies, and 9 per cent of S0/a galaxies were detected in emission. From a comparison of cluster and supercluster field galaxies, we conclude that the frequency of emission-line galaxies (ELGs; W>=20{AA}) is similar for field and cluster early-type galaxies. A similar result has previously been obtained for galaxies of types Sa and later. Together, these results confirm the inference of Biviano et al. (1997A&A...321...84B) that the relative frequency of ELGs in clusters and the field can be entirely accounted for by the different mix of morphological types between the differing environments, and that, for galaxies of a given morphological type, the fraction of ELGs is independent of environment. Detected emission is classified as 'compact' or 'diffuse', identified as circumnuclear starburst or active galactic nucleus (AGN) emission and disc emission, respectively. By comparing spectroscopic data for cluster early-type ELGs with data for field galaxies from the Palomar spectroscopic survey of nearby galactic nuclei, we demonstrate that there is modest evidence for an enhancement of compact H II emission relative to AGN emission in the early-type cluster ELGs as compared to the field. For the cluster early-type galaxies, compact H II emission correlates strongly with a disturbed morphology. This suggests that, as for later-type cluster galaxies, this enhanced compact H II emission can readily be explained as an enhancement of circumnuclear starburst emission due to gravitational tidal interactions, most likely caused by subcluster merging and other on-going processes of cluster virialization.
Neutral hydrogen represents the major observable baryonic constituent of galaxies that fuels the formation of stars through transformation of molecular hydrogen. The emission of the hydrogen recombination line H{alpha} is the most direct tracer of the process that transforms gas (fuel) into stars. We continue to present H{alpha}3 (acronym for H{alpha}-{alpha}{alpha}), an extensive H{alpha}+[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 (SPM) observatory (Mexico). In 48 nights since 2011 we were able to carry out the H{alpha} imaging observations of 724 galaxies in the region of the Coma supercluster 10h<RA<16h ; 24{deg}<Dec<28{deg} and 3900<cz<9000km/s. Of these, 603 are selected from the 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 types (spirals vs. dwarf Irr), over a wide range of stellar mass (~10^8^-10^11.5^M_{sun}_) in the Coma supercluster. The present Paper V provides H{alpha} data and derived star formation rates for the observed galaxies.
UBVI and H{alpha} photometry is presented for 17319 stars in vicinity of the young double cluster h and {chi} Persei. Our photometry extends over a 37'x1{deg} field centered on the association. We construct reddening contours within the imaged field. We find that the two clusters share a common distance modulus of 11.75+/-0.05 and ages of log[age(yr)]=7.1+/-0.1. From the V-H{alpha} color, a measure of the H{alpha} emission strength, we conduct a survey for emission line objects within the association. We detect a sample of 33 Be stars, eight of which are new detections. We present a scenario of evolutionary enhancement of the Be phenomenon to account for the peak in Be fraction toward the top of the main sequence in the population of h and {chi} Persei and similar young clusters. UBVI and H{alpha} photometry was performed on five nights between 1999 August 17 and 25 at the San Diego State University Mount Laguna Observatory with the 1m telescope and a Loral 2048x2048 CCD.
Properties of HII region populations in spiral galaxies provide important information about the physics of star formation as well as regional turbulent motions in the interstellar medium. We present a set of 376 photometrically calibrated HII regions in the nearby late-type spiral galaxy NGC 628. We have studies the mean velocity and velocity dispersion for the H-alpha-emitting gas in NGC 628 and found with widely distributed star formation in the disc plane. The H-alpha emission from the HII regions dominates any emission from the diffuse component in this galaxy.
The galaxy NGC6384 has been observed with an IPCS through H{alpha} and [NII] narrow-band interference filters for direct imagery with the 2.6-m Byurakan telescope. We studied the main physical parameters of the identified 98 HII regions, their diameter and luminosity functions, as well the [NII]/H{alpha} ratio distribution.
Line intensities, visual extinction, abundances and ionization hardness parameter for HII regions in two spiral galaxies are presented. The following galaxies have been observed: NGC 5457 and NGC 4395. In NGC 5457 have been obtained data for 338 regions. In NGC 4395 have been obtained data for 158 regions. For each region position, visual extinction, H-alpha flux, H-alpha equivalent width, H-beta flux, H-beta equivalent width, [OII] flux, [OIII] flux, [SII] flux, [SIII] flux (only for NGC 5457), R23 parameter, oxygen abundance and ionization hardness parameter (only for NGC 5457) are given.
Using the data from the NOAO Local Group Survey, we have measured the H{alpha} fluxes of 291 nebulae associated with 21 of the van den Bergh OB associations. We have combined these data together with six-color HST WFPC2 photometry, in order to identify the most UV-bright stars in the region. The simple purpose of this article is to explore the spatial relationships between these components.
We have identified a total of 1272 newly recognized emission regions in M33. Combined with the previously cataloged total of 1066 H II regions and supernova remnants, this brings M33's total to 2338 emission regions. This paper provides photometry of the new objects in H{alpha}, which is combined with data from previous catalogs to produce a global H II region luminosity function (corrected for incompleteness) that reaches a faint luminosity limit of 2x10^34^ergs/s and shows a broad maximum with a peak frequency at luminosities of 6x10^35^ergs/s. We also plot the H II region size distribution and comment on unusual morphologies.
Nineteen H{alpha} photographs and a catalogue of HII regions in the northern Milky Way are presented. This atlas reveals 85 new regions of faint emission.
We present the first results of a narrow-band photometric study of the massive galaxy cluster XMMU J2235.3-2557 at z=1.39. We obtained deep H narrow-band imaging with the Near InfraRed Imager and Spectrometer on Gemini North, corresponding to H{alpha} emission at the cluster's redshift. Our sample consists of 82 galaxies within a radius of ~500kpc, 10 of which are spectroscopically confirmed cluster members. 16 galaxies are identified as excess line-emitters.
