arXiv subjects

D. Clements

Publications and source records attributed to D. Clements.

44 records · Page 3Linked to original sources

arXiv2003

Sub-millimeter emission from type Ia supernova host galaxies at z=0.5

We present deep sub-millimetre observations of seventeen galaxies at z=0.5, selected through being hosts of a type 1a supernova. Two galaxies are detected directly, and the sample is detected statistically with a mean 850 micron flux of 1.01mJy +/- 0.33mJy, which is 25% - 135% higher than locally. We infer that the mean value of A_v in normal galaxies at z=0.5 is comparable to or greater than the mean A_v in local normal galaxies, in agreement with galaxy chemical evolution models and indirect observational evidence. Scaling from the local value given by Rowan-Robinson (2003) gives a mean extinction at z=0.5 of A_v = 0.56 +/- 0.17. The dust in the brightest sub-mm object in our sample is best interpreted as normal `cirrus' dust similar to that seen locally. The detection rate of our sample suggests that some sources found in blank-field sub-mm surveys may not be high redshift starbursts, but rather cirrus galaxies at moderate redshifts and with lower star formation rates. Finally, an increase in host dust extinction with redshift may impact the cosmological results from distant supernova searches. This emphasizes the need to carefully monitor dust extinction when using type Ia supernovae to measure the cosmological parameters.

astro-ph↗

arXiv2003

INTEGRAL Field Spectroscopy of the Extended Ionized Gas in Arp 220

Integral field optical spectroscopy with the INTEGRAL system has been used to investigate for the first time the two-dimensional kinematic and ionization properties of the extended, warm ionized gas in Arp 220 over an area of 28 kpc by 15 kpc. The structure of the ionized gas is divided into well identified regions associated with the X-ray emitting plumes and extended lobes. Changes in the ionization state of the gas along the major axis of the plumes are detected, in particular in the outer regions of the northwestern plume where the transition between the main stellar body of the galaxy and a broad, low surface brightness tidal tail is located. If the plumes are produced by a starburst-driven galactic wind, the efficiency in the conversion of mechanical to radiation energy is a factor of at least 10 smaller than in galactic winds developed in edge-on spirals with well defined rotation and outflowing axis. The kinematic properties of the lobes are to a first order in agreement with the predictions of the merger scenario according to which the lobes are tidal-induced gas condensations produced during the merging process. The largest velocity gradients and velocity deviations from the systemic velocity are not associated with the plumes, but with the outer stellar envelope and broad tidal tails at distances of up to 7.5 kpc, indicating that the large scale kinematics of the extended ionized gas in Arp 220, is most likely dominated by the tidal-induced motions, and not by galactic winds associated with nuclear starbursts.

astro-ph↗

arXiv2003

Starburst and AGN activity in ultraluminous infrared galaxies

(Abridged) We examine the power source of 41 local Ultraluminous Infrared Galaxies using archival infrared and optical photometry. We fit the observed Spectral Energy Distributions (SEDs) with starburst and AGN components; each component being drawn from a family of templates. We find all of the sample require a starburst, whereas only half require an AGN. In 90% of the sample the starburst provides over half the IR emission, with a mean fractional luminosity of 82%. When combined with other galaxy samples we find that starburst and AGN luminosities correlate over 6 decades in IR luminosity suggesting that a common factor governs both luminosities, plausibly the gas masses in the nuclear regions. We find that the mid-IR 7.7 micron line-continuum ratio is no indication of the starburst luminosity, or the fractional AGN luminosity, and therefore that this ratio is not a reliable diagnostic of the power source in ULIRGs. We propose that the scatter in the radio-IR correlation in ULIRGs is due to a skewed starburst IMF and/or relic relativistic electrons from a previous starburst, rather than contamination from an obscured AGN. We show that most ULIRGs undergo multiple starbursts during their lifetime, and by inference that mergers between more than two galaxies may be common amongst ULIRGs. Our results support the evolutionary model for ULIRGs proposed by Farrah et al 2001, where they can follow many different evolutionary paths of starburst and AGN activity in transforming merging spiral galaxies into elliptical galaxies, but that most do not go through an optical QSO phase. The lower level of AGN activity in our local sample than in z~1 HLIRGs implies that the two samples are distinct populations. We postulate that different galaxy formation processes at high-z are responsible for this difference.

astro-ph↗

arXiv2002

The host galaxies of type Ia supernovae at z=0.6

We examine the host galaxies of high redshift type Ia supernovae (SNe Ia) using archival I and R band data from the Hubble Space Telescope. The SNe Ia host galaxies show a wide variety of morphologies, including undisturbed ellipticals, spirals and disturbed systems. SNe Ia are also found over a wide range of projected distances from the host galaxy centres, ranging from 3kpc to 30kpc. For a sample of 22 SNe Ia at = 0.6, 70% are found in spiral galaxies and 30% are found in elliptical systems, similar to the proportions observed locally. Including additional previously published data, we find no significant difference in the average light-curve-shape-corrected peak B band magnitudes for high-z SNe Ia between spirals and ellipticals. These results are consistent with predictions based on the locally-derived understanding of SNe Ia physics and the influence of progenitor mass and metallicity. We also construct colour maps for two host galaxies and find that both show a non-uniform colour structure with typical variations of rest-frame B-V~0.5. This is most plausibly attributed to the presence of, and variation in dust extinction in these galaxies. Moreover, we find no evidence that the SNe Ia are preferentially found in outer regions (>10kpc) of the host galaxies where extinction would be low. This suggests that the range of host galaxy extinctions of SNe Ia at z~0.6 should be comparable to those of local SNe Ia. Although observational bias cannot be completely ruled out, this appears to be in conflict with the finding of low extinction for SNe Ia found in the high-z supernova search studies.

astro-ph↗

arXiv2001

Ultraluminous Infrared Galaxies: Atlas of Near-Infrared Images

A sample of 27 ultraluminous infrared galaxy (ULIRG) systems has been imaged at 1.6 microns using the HST Near Infrared Camera and Multi-Object Spectrometer (NICMOS). These ULIRGs are from a larger sample also imaged with HST in the I-band. Images and catalog information for the NICMOS subsample, as well as brief morphological descriptions of each system are presented. Inspection of the infrared images and a comparison with optical images of these systems shows that at least 85% are obviously composed of two or more galaxies involved in a close interaction or merger event, with as many as 93% showing some signs of interaction history. Approximately 37% of the systems show either spectroscopic or morphological characteristics of an active galactic nucleus (AGN). The infrared morphologies of these systems are generally less complicated or disturbed than their optical morphologies, indicating that some of the small-scale features seen in optical images are likely due to complicated patterns of dust obscuration, as well as widely distributed star formation activity. In some systems the high-resolution HST infrared images have revealed nuclear remnants that are obscured or unidentified in ground-based imaging, which has led to changes in previously determined interaction stage classifications or system content. In general, however, the NICMOS images support previous conclusions from previous HST optical imaging.

astro-ph↗

arXiv1999

A Morphological Classification Scheme for ULIRGs: Evidence for Multiple Mergers

We have used the Hubble Space Telescope (HST) to study a large sample of ultraluminous IR galaxies (ULIRGs). With a rich legacy database of 150 high-resolution images, we are studying the fine-scale structure of this unique collection of violently starbursting systems. We review here some of the latest results from our survey. We present a simple morphological classification scheme, consisting of 4 ULIRG classes, showing that there is very little luminosity variation (in the mean) between the classes, and that there is equal likelihood of a ULIRG being a recent merger (single) as an on-going collision (multiple). It now appears that the fraction of ULIRGs that show evidence for interaction or merging is very close to 100%. A star-like nucleus is seen in about 15% of the ULIRGs, for which the dominant power source may be a dust-enshrouded AGN/QSO. Many of the results on ULIRGs are pointing to a complicated dynamical history for this sample of galaxies. One possible explanation for this dynamical diversity is the multiple-merger model proposed by Taniguchi & Shioya (1998, ApJ, 501, L167). We present strong observational evidence for multiple mergers among a large fraction of our ULIRG sample. If this is a valid model, then ULIRGs could be the merger remnants of an earlier generation of compact groups of galaxies.

astro-ph↗

arXiv1998

HST NICMOS and WFPC2 Imaging of Ultraluminous Galaxies

HST is used to study the power sources and the interaction-induced tidal disturbances within the most luminous galaxies in the local universe -- the Ultra-Luminous IR Galaxies (ULIRGs) -- through the use of I-band images with WFPC2 and H-band images with NICMOS. Such images are probing for the first time the fine-scale structures in the strong collision-disturbed morphologies of these rare and exotic galaxies.

astro-ph↗

arXiv1997

The Double Quasar Q2138-431: Lensing by a Dark Galaxy?

We report the discovery of a new gravitational lens candidate Q2138-431AB, comprising two quasar images at a redshift of 1.641 separated by 4.5 arcsecs. The spectra of the two images are very similar, and the redshifts agree to better than 115 km.sec$^{-1}$. The two images have magnitudes $B_J = 19.8$ and $B_J = 21.0$, and in spite of a deep search and image subtraction procedure, no lensing galaxy has been found with $R < 23.8$. Modelling of the system configuration implies that the mass-to-light ratio of any lensing galaxy is likely to be around $1000 M_{\odot}/L_{\odot}$, with an absolute lower limit of $200 M_{\odot}/L_{\odot}$ for an Einstein-de Sitter universe. We conclude that the most likely explanation of the observations is gravitational lensing by a dark galaxy, although it is possible we are seeing a binary quasar.

astro-ph↗