Continuum removal in Hα extragalactic measurements

Spector, O.; Finkelman, Ido; Brosch, Noah

doi:10.1111/j.1365-2966.2011.19869.x

Cited by 36 publications

(46 citation statements)

References 23 publications

(32 reference statements)

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“…The images were registered in the J2000 epoch equatorial coordinate system using the Two Micron All Sky Survey (2MASS) images. The underlying stellar continuum in the Hα filter is subtracted using the standard procedure given by Waller (1990) and Spector et al (2012). The Wide to Narrow Continuum Ratio (WNCR) is determined using nonsaturated, non-variable field stars in the CCD image.…”

Section: Observations and Resultsmentioning

confidence: 99%

“…The Hα equivalent width, defined as the ratio of Hα flux and specific continuum flux at the wavelength of Hα emission, is obtained following the standard procedure given by Spector et al (2012). The specific continuum flux is total continuum flux minus Hα line contribution within the Hα filter divided by its area (1.07×T N,max ×F W HM N ).…”

Section: Observations and Resultsmentioning

confidence: 99%

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Devasthal Fast Optical Telescope Observations of Wolf–Rayet Dwarf Galaxy Mrk 996

Jaiswal

Omar

2013

J Astrophys Astron

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Abstract.The Devasthal Fast Optical Telescope (DFOT) is a 1.3 meter aperture optical telescope, recently installed at Devasthal, Nainital. We present here the first results using an Hα filter with this telescope on a Wolf-Rayet dwarf galaxy Mrk 996. The instrumental response and the Hα sensitivity obtained with the telescope are (3.3 ± 0.3) × 10 −15 (erg s −1 cm −2 )/(counts s −1 ) and 7.5×10 −17 erg s −1 cm −2 arcsec −2 respectively. The Hα flux and the equivalent width for Mrk 996 are estimated as (132 ± 37) × 10 −14 erg s −1 cm −2 and ∼96Å respectively. The star formation rate is estimated as 0.4 ± 0.1 M ⊙ yr −1 . Mrk 996 deviates from the radio-FIR correlation known for normal star forming galaxies with a deficiency in its radio continuum. The ionized gas as traced by Hα emission is found in a disk shape which is misaligned with respect to the old stellar disk. This misalignment is indicative of a recent tidal interaction in the galaxy. We believe that galaxy-galaxy tidal interaction is the main cause of the WR phase in Mrk 996.

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Section: Observations and Resultsmentioning

confidence: 99%

Section: Observations and Resultsmentioning

confidence: 99%

Devasthal Fast Optical Telescope Observations of Wolf–Rayet Dwarf Galaxy Mrk 996

Jaiswal

Omar

2013

J Astrophys Astron

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“…This can be due to ionization from AGNs, or from red and old PAGB stars (Stasińska et al 2008) or a technical artifact due to improper normalization of the OFF-band images. Indeed, as pointed out by Spector et al (2012), the normalization coefficient of the r-on the narrow-band image strongly depends on the color of the galaxy. We calibrated our normalization for blue galaxies ( g − r = 0.4) because our sample is dominated by blue dwarfs.…”

Section: Ew/r Parametermentioning

confidence: 99%

“…4. Computing the effective radius in the EW image makes the central emission of giant spirals (which we expect to be the most contaminated by [NII] (Paper I) and dust extinction issues) less dominant than the outer disk emission, where the metallicity is lower (Zaritsky et al 1994;Skillman et al 1996) and the blue color provides a better continuum removal (Spector et al 2012). Using EW/r increases the trend of the average values for unperturbed galaxies in bins of Hubble type than when using r e (Hα); (see Fig.…”

Section: Spatial Growth Of Galaxiesmentioning

confidence: 99%

Hα3: an Hαimaging survey of HI selected galaxies from ALFALFA

Fossati

Gavazzi

Savorgnan

et al. 2013

A&A

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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 (<10 Myr) and the old (>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 (De f HI ) that we use to divide the sample in unperturbed galaxies (De f HI ≤ 0.3) and perturbed galaxies (De f HI > 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.

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“…2). The ON-and OFF-band frames are scaled using ad-hoc normalisation factors n, depending on the typical colour of the galaxy (Spector et al 2012). The colour-dependent normalisation was determined using 15 stars of different colour in the observed field.…”

Section: Narrow-band Imagingmentioning

confidence: 99%

Spectacular tails of ionized gas in the Virgo cluster galaxy NGC 4569

Boselli

Cuillandre

Fossati

et al. 2016

A&A

128

169

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Using MegaCam at the CFHT, we obtained a deep narrow band Hα+ [NII] wide-field image of NGC 4569 (M90), the brightest late-type galaxy in the Virgo cluster. The image reveals the presence of long tails of diffuse ionized gas, without any associated stellar component extending from the disc of the galaxy up to 80 kpc (projected distance) and with a typical surface brightness of a few 10 −18 erg s −1 cm −2 arcsec −2 . These features provide direct evidence that NGC 4569 is undergoing a ram-presure stripping event. The image also shows a prominent 8 kpc spur of ionized gas that is associated with the nucleus that spectroscopic data identify as an outflow. With some assumptions on the 3D distribution of the gas, we use the Hα surface brightness of these extended low-surface brightness features to derive the density and the mass of the gas that has been stripped during the interaction of the galaxy with the intracluster medium. The comparison with ad hoc chemo-spectrophotometric models of galaxy evolution indicates that the mass of the Hα emitting gas in the tail is a large fraction of that of the cold phase that has been stripped from the disc, suggesting that the gas is ionized within the tail during the stripping process. The lack of star-forming regions suggests that mechanisms other than photoionization are responsible for the excitation of the gas (shocks, heat conduction, magneto hydrodynamic waves). This analysis indicates that ram pressure stripping is efficient in massive (M star 10 10.5 M ) galaxies located in intermediate-mass ( 10 14 M ) clusters under formation. It also shows that the mass of gas expelled by the nuclear outflow is only ∼1% than that removed during the ram pressure stripping event. Together these results indicate that ram pressure stripping, rather than starvation through nuclear feedback, can be the dominant mechanism that is responsible for the quenching of the star formation activity of galaxies in high density environments.Key words. galaxies: individual: NGC 4569 -galaxies: clusters: general -galaxies: clusters: individual: Virgo -galaxies: evolutiongalaxies: interactions -galaxies: ISM Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canadian-French-Hawaii Telescope (CFHT) which is operated by the

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Continuum removal in Hα extragalactic measurements

Cited by 36 publications

References 23 publications

Devasthal Fast Optical Telescope Observations of Wolf–Rayet Dwarf Galaxy Mrk 996

Devasthal Fast Optical Telescope Observations of Wolf–Rayet Dwarf Galaxy Mrk 996

Hα3: an Hαimaging survey of HI selected galaxies from ALFALFA

Spectacular tails of ionized gas in the Virgo cluster galaxy NGC 4569

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