Kisha Delain - Academia.edu (original) (raw)

Papers by Kisha Delain

This paper discusses a pilot program using real data from our university telescope in laboratory ... more This paper discusses a pilot program using real data from our university telescope in laboratory exercises with our students at the University of St. Thomas. In this paper, I evaluate the effectiveness of these labs and their impact on student attitudes using standardized learning assessments combined with student interviews and surveys. One hundred and sixteen undergraduate students enrolled our fall introductory astronomy course completed our newly developed exercises as a normal part of the laboratory portion of the introductory astronomy course, with comparison groups utilizing "canned" or simulated data. Student attitudes improved in the treatment group more than in the comparison group in both questions of interest: how students feel about science, and whether or not students feel they can do science. In addition, student content knowledge gains are about 10% higher in treatment groups than in comparison groups.

We present an overview of unbiased studies of diffuse extragalactic radio sources. We use a previ... more We present an overview of unbiased studies of diffuse extragalactic radio sources. We use a previously developed filtering technique to remove compact sources from large surveys such as WENSS, WISH, and NVSS and examine the residual diffuse emission. A search of these residuals, unbiased by optical or X-ray selection, has uncovered a wide variety of diffuse sources, including those associated with groups of galaxies, ``blank'' fields, and previously unrecognized diffuse radio galaxy emission, as well as halos and relics of rich clusters. A second, targeted survey of the brightest X-ray clusters results in a number of new sources, and illuminates some important selection effects. When the well-established relationship between X-ray and radio halo luminosities is extrapolated to lower levels, the apparent correlation holds quite well for any type of diffuse source, even background noise. The observed correlations must therefore be scrutinized for possible selection effects bef...

Received <date>; accepted <date>; published online <date> Abstract. We present ... more Received <date>; accepted <date>; published online <date> Abstract. We present an overview of unbiased studies of diffuse extragalactic radio sources. We use a previously developed filtering technique to remove compact sources from large surveys such as WENSS, WISH, and NVSS and examine the residual diffuse emission. A search of these residuals, unbiased by optical or X-ray selection, has uncovered a wide variety

Received <date>; accepted <date>; published online <date> Abstract. We have dis... more Received <date>; accepted <date>; published online <date> Abstract. We have discovered new diffuse radio sources likely associated with groups of galaxies at low redshift (0.01-0.04) and without apparent AGN by using the WENSS and WISH catalogs to perform an unbiased survey. These sources resemble the radio halos, mini-halos, and ’relics ’ of rich clusters, which are thought to be powered by shocks and turbulence

We report on the population of point sources discovered during an 18.5 ksec Chandra ACIS-S observ... more We report on the population of point sources discovered during an 18.5 ksec Chandra ACIS-S observation of the Sombrero Galaxy. We present the luminosity function, the spectra of the 6 brightest sources, consider correlations with globular clusters (GCs) and with planetary nebulae (PNe), and study the galaxy's population of SSSs. We detected 122 sources, 22 of them are identified as luminous supersoft X-ray sources (SSSs). There is an over density of SSSs within 1.5 kpc of the nucleus, which is itself the brightest X-ray source. SSSs are also found in the disk and halo, with 1 SSS in a globular cluster (GC). Several sources in Sombrero's halo are good candidates for SSS models in which the accretor is a nuclear-burning white dwarf. In total, 32 X-ray sources are associated with GCs. The majority of sources with luminosity > 1e38 erg/s are in GCs. These results for M104, an Sa galaxy, are similar to what has been found for elliptical galaxies and for the late-type spiral M31. We find that those optically bright GCs with X-ray sources house only the brightest X-ray sources. We find that, in common with other galaxies, there appears to be a positive connection between young (metal-rich) GCs and X-ray sources, but that the brightest X-ray sources are equally likely to be in metal-poor GCs. We propose a model which can explain the trends seen in the data sets from the Sombrero and other galaxies. Thermal-time scale mass transfer can occur in some of the the younger clusters in which the turn-off mass is slightly greater than 0.8Modot0.8 M_\odot0.8Modot; multiplicity may play a role in some of the most massive clusters; accretion from giant stars may be the dominant mechanism in some older, less massive and less centrally concentrated clusters.

We present results from a deep, low resolution VLA observation of the TONS 6o by 6o field at 90cm... more We present results from a deep, low resolution VLA observation of the TONS 6o by 6o field at 90cm, and a possible detection of large scale structure in diffuse radio emission. Other studies have identified >100 Mpc superstructures in this field. We present the results of pushing into the radio confusion limit by subtracting small sources detected at higher resolution. We have removed ˜95% of the flux from the small sources using this method. We discuss the prospects of detecting large scale structure through the radio emission expected to be generated by structure formation shocks. Partial support has been provided by NSF Grant AST-0307600 to the University of Minnesota.

The Astrophysical Journal, 2003

We report on the population of point sources discovered during an 18.5 ksec Chandra ACIS-S observ... more We report on the population of point sources discovered during an 18.5 ksec Chandra ACIS-S observation of the Sombrero Galaxy. We present the luminosity function, the spectra of the 6 brightest sources, consider correlations with globular clusters (GCs) and with planetary nebulae (PNe), and study the galaxy's population of SSSs. We detected 122 sources, 22 of them are identified as luminous supersoft X-ray sources (SSSs). There is an over density of SSSs within 1.5 kpc of the nucleus, which is itself the brightest X-ray source. SSSs are also found in the disk and halo, with one SSS in a globular cluster (GC). This source is somewhat harder than most SSSs; the energy distribution of its photons is consistent with what is expected from an accreting intermediate mass black hole. Several sources in Sombrero's halo are good candidates for SSS models in which the accretor is a nuclear-burning white dwarf. In total, 32 X-ray sources are associated with GCs. The majority of sources with luminosity > 10 38 erg s −1 are in GCs. These results for M104, an Sa galaxy, are similar to what has been found for elliptical galaxies and for the late-type spiral M31. We find that those optically bright GCs with X-ray sources house only the brightest X-ray sources. We find that, in common with other galaxies, there appears to be a positive connection between young (metal-rich) GCs and X-ray sources, but that the brightest X-ray sources are equally likely to be in metal-poor GCs. The luminosity function of X-ray sources in GCs has a cut-of near the Eddington luminosity for a 1.4 M ⊙ object. We propose a model which can explain the trends seen in the data sets from the Sombrero and other galaxies. Thermal-time scale mass transfer can occur in some of the the younger clusters in which the turn-off mass is slightly greater than 0.8 M ⊙ ; multiplicity may play a role in some of the most massive clusters; accretion from giant stars may be the dominant mechanism in some older, less massive and less centrally concentrated clusters. Key elements of the model can be tested.

New Astronomy Reviews, 2001

Hard X-ray selection is, arguably, the optimal method for defining a representative sample of act... more Hard X-ray selection is, arguably, the optimal method for defining a representative sample of active galactic nuclei (AGN). Hard X-rays are unbiased by the affects of obscuration and reprocessing along the line-of-sight intrinsic/external to the AGN which result in unknown fractions of the population being missed from traditional optical/soft-X-ray samples. We present the farinfrared (IR) observations of 21 hard X-ray selected AGN from the HEAO-1 A2 sample observed with ISO. We characterize the far-infrared (IR) continua of these X-ray selected AGN, compare them with those of various radio and optically selected AGN samples and with models for an AGN-heated, dusty disk. The X-ray selected AGN show broad, warm IR continua covering a wide temperature range (∼ 20 − 1000 K in a thermal emission scenario). Where a far-IR turnover is clearly observed, the slopes are < 2.5 in all but three cases so that non-thermal emission remains a possibility, although the presence of cooler dust resulting in a turnover at wavelengths longwards of the ISO range is considered more likely. The sample also shows a wider range of optical/UV shapes than the optically/radio-selected samples, extending to redder near-IR colors. The bluer objects are type 1 Seyferts, while the redder AGN are mostly intermediate or type 2 Seyferts. This is consistent with a modified unification model in which obscuration increases as we move from a face-on towards more edge-on line-of-sight (l.o.s.) However, this relation does not extend to the mid-infrared as the 25µm/60µm ratios are similar in Seyferts with differing type and optical/UV reddening. The resulting limits on the column density of obscuring material through which we are viewing the redder AGN (N H ∼ 10 22 cm −2) are inconsistent with standard optically thick torus models (N H ∼ 10 24 cm −2) and simple unification models. Instead our results support more complex models in which the amount of obscuring material increases with viewing angle and may be clumpy. Such a scenario, already suggested by differing optical/near-IR spectroscopic and X-ray AGN classifications, allows for different amounts of obscuration of the continuum emission in different wavebands and of the broad emission line region which, in turn, results in a mixture of behaviors for AGN with similar optical emission line classifications. The resulting decrease in the optical depth of the obscuring material also allows the AGN to heat more dust at larger radial distances. We show that an AGN-heated, flared, dusty disk with mass ∼ 10 9 M and size∼few hundred pc is able to generate optical−far-IR spectral energy distributions (SEDs) which reproduce the wide range of SEDs present in our sample with no need for an additional starburst component to generate the long-wavelength, cooler part of the IR continuum. −0.01 42.96 +0.00 −0.00 43.63 +0.00 −0.00 44.22 +0.11 −0.11 44.13 +0.14 −0.13 44.11 +0.11 −0.14 45.19 +0.10 −0.11 MKN 590 44.36 +0.05 −0.05 44.20 +0.04 −0.04 44.23 +0.01 −0.02 43.86 +0.02 −0.02 44.05 +0.20 −0.20 43.61 +0.14 −0.14 45.16 +0.09 −0.14 ESO 198-G24 43.99 +0.10 −0.14 43.76 +0.04 −0.06 43.78 +0.00 −0.00 44.02 +0.01 −0.01 44.77 +0.04 −0.03 ... 45.29 +0.07 −0.11 3A 0557-383 43.26 +0.08 −0.13 43.52 +0.11 −0.16 43.79 +0.13 −0.20 44.07 +0.14 −0.21 42.95 +0.01 −0.01 43.89 +0.09 −0.09 45.31 +0.09 −0.10 PG 0804+761 45.53 +0.22 −0.20 45.47 +0.04 −0.04 45.01 +0.02 −0.03 44.83 +0.04 −0.05 44.82 +0.27 −0.22 44.53 +0.10 −0.10 46.27 +0.14 −0.12 H1039-074 46.02 +0.01 −0.01 45.96 +0.01 −0.01 45.72 +0.02 −0.02 45.57 +0.02 −0.03 ... ... 47.38 +0.11 −0.04 NGC 3783 43.88 +0.01 −0.01 44.02 +0.01 −0.01 43.82 +0.02 −0.02 43.20 +0.02 −0.02 42.95 +0.11 −0.08 43.18 +0.10 −0.10 44.86 +0.02 −0.02 TON 1542 44.99 +0.02 −0.03 44.84 +0.03 −0.03 44.47 +0.04 −0.06 44.39 +0.09 −0.10 44.62 +0.05 −0.05 43.90 +0.05 −0.05 45.75 +0.

Astronomische Nachrichten, 2006

The Astrophysical Journal, 2003

We report on the population of point sources discovered during an 18.5 ksec Chandra ACIS-S observ... more We report on the population of point sources discovered during an 18.5 ksec Chandra ACIS-S observation of the Sombrero Galaxy. We present the luminosity function, the spectra of the 6 brightest sources, consider correlations with globular clusters (GCs) and with planetary nebulae (PNe), and study the galaxy's population of SSSs. We detected 122 sources, 22 of them are identified as luminous supersoft X-ray sources (SSSs). There is an over density of SSSs within 1.5 kpc of the nucleus, which is itself the brightest X-ray source. SSSs are also found in the disk and halo, with one SSS in a globular cluster (GC). This source is somewhat harder than most SSSs; the energy distribution of its photons is consistent with what is expected from an accreting intermediate mass black hole. Several sources in Sombrero's halo are good candidates for SSS models in which the accretor is a nuclear-burning white dwarf. In total, 32 X-ray sources are associated with GCs. The majority of sources with luminosity > 10 38 erg s −1 are in GCs. These results for M104, an Sa galaxy, are similar to what has been found for elliptical galaxies and for the late-type spiral M31. We find that those optically bright GCs with X-ray sources house only the brightest X-ray sources. We find that, in common with other galaxies, there appears to be a positive connection between young (metal-rich) GCs and X-ray sources, but that the brightest X-ray sources are equally likely to be in metal-poor GCs. The luminosity function of X-ray sources in GCs has a cut-of near the Eddington luminosity for a 1.4 M ⊙ object. We propose a model which can explain the trends seen in the data sets from the Sombrero and other galaxies. Thermal-time scale mass transfer can occur in some of the the younger clusters in which the turn-off mass is slightly greater than 0.8 M ⊙ ; multiplicity may play a role in some of the most massive clusters; accretion from giant stars may be the dominant mechanism in some older, less massive and less centrally concentrated clusters. Key elements of the model can be tested.

New Astronomy Reviews, 2001

Astronomische Nachrichten, 2006