arXiv subjects

Eliot M. Malumuth

Publications and source records attributed to Eliot M. Malumuth.

7 recordsLinked to original sources

arXiv2017

Optical Coronagraphic Spectroscopy of AU Mic: Evidence of Time Variable Colors?

We present coronagraphic long slit spectra of AU Mic's debris disk taken with the STIS instrument aboard the Hubble Space Telescope (HST). Our spectra are the first spatially resolved, scattered light spectra of the system's disk, which we detect at projected distances between approximately 10 and 45 AU. Our spectra cover a wavelength range between 5200 and 10200 angstroms. We find that the color of AU Mic's debris disk is bluest at small (12-35 AU) projected separations. These results both confirm and quantify the findings qualitatively noted by Krist et al. (2005), and are different than IR observations that suggested a uniform blue or gray color as a function of projected separation in this region of the disk. Unlike previous literature that reported the color of AU Mic's disk became increasingly more blue as a function of projected separation beyond approximately 30 AU, we find the disk's optical color between 35-45 AU to be uniformly blue on the southeast side of the disk and decreasingly blue on the northwest side. We note that this apparent change in disk color at larger projected separations coincides with several fast, outward moving "features" that are passing through this region of the southeast side of the disk. We speculate that these phenomenon might be related, and that the fast moving features could be changing the localized distribution of sub-micron sized grains as they pass by, thereby reducing the blue color of the disk in the process. We encourage follow-up optical spectroscopic observations of the AU Mic to both confirm this result, and search for further modifications of the disk color caused by additional fast moving features propagating through the disk.

astro-ph.SR↗

arXiv2004

HST-STIS Spatially Resolved Spectroscopy and Coronagraphic Imaging of the TW Hydrae Circumstellar Disk

We present the first spatially resolved spectrum of scattered light from the TW Hydrae protoplanetary disk. This nearly face-on disk is optically thick, surrounding a classical T Tauri star in the nearby 10 Myr old TW Hya association. The spectrum was taken with the HST-STIS CCD, providing resolution R ~ 360 over the wavelength range 5250 - 10300 A. Spatially resolved spectroscopy of circumstellar disks is difficult due to the high contrast ratio between the bright star and faint disk. Our novel observations provide optical spectra of scattered light from the disk between 40 AU and 155 AU from the star. The scattered light has the same color as the star (gray scattering) at all radii, except the innermost region. This likely indicates that the scattering dust grains are larger than about 1 micron all the way out to large radii. From the spectroscopic data, we also obtained radial profiles of the integrated disk brightness at two position angles, over almost the same region as previously observed in HST-WFPC2 and NICMOS coronagraphic images (35 AU to 173 AU from the star). The profiles have the same shape as the earlier ones, but show a small azimuthal asymmetry in the disk not previously noted. Our STIS broad-band coronagraphic images of TW Hya confirm the reality of this asymmetry, and show that the disk surface brightness interior to 140 AU has a sinusoidal dependence on azimuthal angle. The maximum brightness occurs at a position angle of 233.6 +/- 5.7 degrees East of North. This might be caused by the combination of forward-scattering and an increase in inclination in the inner region of the disk, suggesting that the TW Hya disk has a warp like that seen in the Beta Pictoris debris disk.

astro-ph↗

arXiv2001

HST-WFPC2 Observations of the Star Clusters in the Giant HII Regions of M33

We present a photometric study of the stars in ionizing star clusters embedded in several giant HII regions of M33 (CC93, IC 142, NGC 595, MA2, NGC 604 and NGC 588). Our photometry are based on the HST-WFPC2 images of these clusters. Color-magnitude diagrams and color-color diagrams of these clusters are obtained and are used for estimating the reddenings and ages of the clusters. The luminosity functions (LFs) and initial mass functions (IMFs) of the massive stars in these clusters are also derived. The slopes of the IMFs range from Gamma = -0.5 to -2.1. It is found interestingly that the IMFs get steeper with increasing galactocentric distance and with decreasing [O/H] abundance.

astro-ph↗

arXiv2000

Wide Field Imaging of the Hubble Deep Field South Region II: The Evolution of Galaxy Clustering at z<1

We present the galaxy-galaxy angular correlations as a function of photometric redshift in a deep-wide galaxy survey centered on the Hubble Deep Field South. Images were obtained with the Big Throughput Camera on the Blanco 4m telescope at CTIO, of 1/2 square degree in broad-band uBVRI, reaching ~24th mag. Approximately 40,000 galaxies are detected in the survey. We determine photometric redshifts using galaxy template fitting to the photometry. Monte Carlo simulations show that redshifts from these data should be reliable out to z~1, where the 4000 Angstrom break shifts into the I-band. The inferred redshift distribution, n(z), shows good agreement with the distribution of galaxies measured in the HDF North and the Canada-France Redshift Survey. After assigning galaxies to redshift bins with width Delta_z=0.33, we determine the two point angular correlation function in each bin. We find that the amplitude of the correlation, A_w, drops across the three bins to redshift z~1. Simple epsilon models of clustering evolution fit this result, with the best agreement for epsilon=0. Hierarchical cold-dark-matter models best fit in a low density, Lambda-dominated universe.

astro-ph↗

arXiv2000

Wide Field Imaging of the Hubble Deep Field-South Region I: Quasar Candidates

We present candidate quasars from a multi-color (uBVRI + narrow-band) imaging survey of 1/2 square degree around the Hubble Deep Field - South. We identify 154 candidate quasars with B < 23 using color selection, consistent with previously measured QSO number counts if we assume a 60% selection efficiency. The narrow-band filter (NB) was centered at 3958 A to detect Ly-alpha at the redshift of J2233-6033, the HDF-S QSO. We confirm the presence of Ly-alpha nebulosity extending ~12'' around the HDF-S QSO, reported by Bergeron et al. (1999). We detect 10 point-like objects in emission through the NB filter. Of these, 7 satisfy our QSO color selection criteria. One of emission-line objects is a B~20 radio-quiet quasar at z=1.56, 6.7' from the line of sight to the HDF-S QSO and ~12'' from the western edge of the WFPC2 deep field.

astro-ph↗

arXiv1999

The H$α$ Luminosity Function and Global Star Formation Rate From Redshifts of One to Two

We present a luminosity function for H$α$ emission from galaxies at redshifts between 0.7 and 1.9 based on slitless spectroscopy with NICMOS on HST. The luminosity function is well fit by a Schechter function over the range $6 \times 10^{41} < L(Hα) < 2 \times 10^{43} erg/sec$ with $L^* = 7 \times 10^{42} erg/sec$ and $ϕ^* = 1.7 \times 10^{-3} Mpc^{-3}$ for $H_0=50 km/s Mpc^{-1}$ and $q_0=0.5$. We derive a volume averaged star formation rate at $z = 1.3 \pm 0.5$ of 0.13 M_{\odot} yr^{-1} Mpc^{-3} without correction for extinction. The SFR that we derive at $\sim 6500 Åis a factor of 3 higher than that deduced from 2800 Åcontinua. If this difference is due entirely to reddening, the extinction correction at 2800 Åis quite significant. The precise magnitude of the total extinction correction at rest-frame UV wavelengths (e.g. 2800 Åand 1500 Å) is sensitive to the relative spatial distribution of the stars, gas and dust, as well as on the extinction law. In the extreme case of a homogeneous foreground dust screen and a MW or LMC extinction law, we derive a total extinction at 2800 Åof 2.1 magnitudes, or a factor of 7 correction to the UV luminosity density. If we use the Calzetti reddening curve, which was derived for the model where stars, gas and dust are well mixed and nebular gas suffers more extinction than stars, our estimate of A$_{2800}$ is increased by more than one magnitude.

astro-ph↗

arXiv1998

Galaxy Morphology from NICMOS Parallel Imaging

We present high resolution NICMOS images of random fields obtained in parallel to other HST observations. We present galaxy number counts reaching H=24. The H-band galaxy counts show good agreement with the deepest I- and K-band counts obtained from ground-based data. We present the distribution of galaxies with morphological type to H<23. We find relatively fewer irregular galaxies compared to an I-band sample from the Hubble Deep Field, which we attribute to their blue color, rather than to morphological K-corrections. We conclude that the irregulars are intrinsically faint blue galaxies at z<1.

astro-ph↗