B. Holwerda - Academia.edu (original) (raw)
Papers by B. Holwerda
The Astrophysical Journal, 2014
The Astrophysical Journal, 2016
Monthly Notices of the Royal Astronomical Society, 2015
The Astrophysical Journal, 2015
Monthly Notices of the Royal Astronomical Society, 2014
Astronomy & Astrophysics, 2014
The halo of NGC 891 has been the subject of studies for more than a decade. One of its most strik... more The halo of NGC 891 has been the subject of studies for more than a decade. One of its most striking features is the large asymmetry in H-$\alpha$ emission. We have taken a quantitative look at this asymmetry at different wavelengths for the first time. We propose that NGC 891 is intrinsically almost symmetric, as seen in Spitzer observations, and the large asymmetry in H-$\alpha$ emission is mostly due to dust attenuation. We quantify the additional optical depth needed to cause the observed H-$\alpha$ asymmetry. A comparison of large strips on the North East side of the galaxy with strips covering the same area in the South West we can quantify and analyze the asymmetry in the different wavelengths. From the 24 mu\mumum emission we find that the intrinsic asymmetry in star-formation in NGC 891 is small i.e., approximately 30%. The additional asymmetry in H-alpha is modeled as additional symmetric dust attenuation which extends up to ~ 40'' (1.9 kpc) above the plane of the ...
Recently, we have developed and calibrated the Synthetic Field Method to derive the total extinct... more Recently, we have developed and calibrated the Synthetic Field Method to derive the total extinction through disk galaxies. The method is based on the number counts and colours of distant background field galaxies that can be seen through the foreground object. Here, we investigate how large (10-m) and very large (20 to 30-m), diffraction-limited, optical and infrared telescopes in space would improve the detection of background galaxies behind Local Group objects, including the Galactic bulge. We find that, besides and perhaps more important than telescope size, a well-behaved, well-characterized PSF would facilitate in general the detection of faint objects in crowded fields, and greatly benefit several other important research areas, like the search for extrasolar planets, the study of quasar hosts and, most relevant for this meeting, the surveying of nearby large-scale structure in the Zone of Avoidance, in particular behind the Galactic bulge.
The Astronomical Journal, 2007
Astronomy and Astrophysics, 2005
Astronomy & Astrophysics, 2013
Astronomy and Astrophysics, 2007
Photometric analysis of backlit galaxies is a powerful way to measure the extinction in disks, bu... more Photometric analysis of backlit galaxies is a powerful way to measure the extinction in disks, but has hitherto been limited by the number of suitable pairs near enough for analysis. New searches of the SDSS imagery (mostly from the public galaxyzoo.org project) have revealed hundreds of candidate pairs, opening the possibility of tracing extinction properties across Hubble type and surface
Photometric analysis of backlit galaxies is a powerful way to measure the extinction in disks, bu... more Photometric analysis of backlit galaxies is a powerful way to measure the extinction in disks, but has hitherto been limited by the number of suitable pairs near enough for analysis. New searches of the SDSS imagery (mostly from the public galaxyzoo.org project) have revealed over 1800 candidate pairs, opening the possibility of tracing extinction properties across Hubble type and surface
ABSTRACT NGC 1097 has an extensive, unique network of jet-like extended structures that stretch o... more ABSTRACT NGC 1097 has an extensive, unique network of jet-like extended structures that stretch out for dozens of kiloparsecs. Their origin has remained a mystery for decades. The evidence for their association with the AGN is weak, and the lack of HI emission in the vicinity makes it unlikely that they are the product of tidal interactions or streams off the main disk of the galaxy. Recent modeling has shown that the structures may be the remnants of a dwarf galaxy, though the type of dwarf remains unclear, and such interactions are complicated by the fact that the main spiral has a large bar. We propose Spitzer observations of these features to determine the streams' true extent, to age-date individual structures by focusing on the old stellar population, estimate their masses, and calculate their metallicities. We will use Spitzer's sensitivity and the degeneracy-breaking IRAC colors to unravel the history of this unusual object. This proposal is part of broader studies by members of this team on galaxy outskirts and interactions, including mergers, streams, shells, asymmetries and lopsidedness, all of which contribute to our understanding of galaxy evolution in the nearby Universe.
The Astrophysical Journal, 2014
The Astrophysical Journal, 2016
Monthly Notices of the Royal Astronomical Society, 2015
The Astrophysical Journal, 2015
Monthly Notices of the Royal Astronomical Society, 2014
Astronomy & Astrophysics, 2014
The halo of NGC 891 has been the subject of studies for more than a decade. One of its most strik... more The halo of NGC 891 has been the subject of studies for more than a decade. One of its most striking features is the large asymmetry in H-$\alpha$ emission. We have taken a quantitative look at this asymmetry at different wavelengths for the first time. We propose that NGC 891 is intrinsically almost symmetric, as seen in Spitzer observations, and the large asymmetry in H-$\alpha$ emission is mostly due to dust attenuation. We quantify the additional optical depth needed to cause the observed H-$\alpha$ asymmetry. A comparison of large strips on the North East side of the galaxy with strips covering the same area in the South West we can quantify and analyze the asymmetry in the different wavelengths. From the 24 mu\mumum emission we find that the intrinsic asymmetry in star-formation in NGC 891 is small i.e., approximately 30%. The additional asymmetry in H-alpha is modeled as additional symmetric dust attenuation which extends up to ~ 40'' (1.9 kpc) above the plane of the ...
Recently, we have developed and calibrated the Synthetic Field Method to derive the total extinct... more Recently, we have developed and calibrated the Synthetic Field Method to derive the total extinction through disk galaxies. The method is based on the number counts and colours of distant background field galaxies that can be seen through the foreground object. Here, we investigate how large (10-m) and very large (20 to 30-m), diffraction-limited, optical and infrared telescopes in space would improve the detection of background galaxies behind Local Group objects, including the Galactic bulge. We find that, besides and perhaps more important than telescope size, a well-behaved, well-characterized PSF would facilitate in general the detection of faint objects in crowded fields, and greatly benefit several other important research areas, like the search for extrasolar planets, the study of quasar hosts and, most relevant for this meeting, the surveying of nearby large-scale structure in the Zone of Avoidance, in particular behind the Galactic bulge.
The Astronomical Journal, 2007
Astronomy and Astrophysics, 2005
Astronomy & Astrophysics, 2013
Astronomy and Astrophysics, 2007
Photometric analysis of backlit galaxies is a powerful way to measure the extinction in disks, bu... more Photometric analysis of backlit galaxies is a powerful way to measure the extinction in disks, but has hitherto been limited by the number of suitable pairs near enough for analysis. New searches of the SDSS imagery (mostly from the public galaxyzoo.org project) have revealed hundreds of candidate pairs, opening the possibility of tracing extinction properties across Hubble type and surface
Photometric analysis of backlit galaxies is a powerful way to measure the extinction in disks, bu... more Photometric analysis of backlit galaxies is a powerful way to measure the extinction in disks, but has hitherto been limited by the number of suitable pairs near enough for analysis. New searches of the SDSS imagery (mostly from the public galaxyzoo.org project) have revealed over 1800 candidate pairs, opening the possibility of tracing extinction properties across Hubble type and surface
ABSTRACT NGC 1097 has an extensive, unique network of jet-like extended structures that stretch o... more ABSTRACT NGC 1097 has an extensive, unique network of jet-like extended structures that stretch out for dozens of kiloparsecs. Their origin has remained a mystery for decades. The evidence for their association with the AGN is weak, and the lack of HI emission in the vicinity makes it unlikely that they are the product of tidal interactions or streams off the main disk of the galaxy. Recent modeling has shown that the structures may be the remnants of a dwarf galaxy, though the type of dwarf remains unclear, and such interactions are complicated by the fact that the main spiral has a large bar. We propose Spitzer observations of these features to determine the streams' true extent, to age-date individual structures by focusing on the old stellar population, estimate their masses, and calculate their metallicities. We will use Spitzer's sensitivity and the degeneracy-breaking IRAC colors to unravel the history of this unusual object. This proposal is part of broader studies by members of this team on galaxy outskirts and interactions, including mergers, streams, shells, asymmetries and lopsidedness, all of which contribute to our understanding of galaxy evolution in the nearby Universe.