Stars in the Hubble Ultra Deep Field

Abstract

We identified 46 unresolved source candidates in the Hubble Ultra Deep Field, down to i775 = 29.5. Unresolved objects were identified using a parameter S, which measures the deviation from the curve-of-growth of a point source. Extensive testing of this parameter was carried out, including the effects of decreasing signal-to-noise and of the apparent motions of stars, which demonstrated that stars brighter than i775 = 27.0 could be robustly identified. Low resolution grism spectra of the 28 objects brighter than i775 = 27.0 identify 18 M and later stellar type dwarfs, 2 candidate L-dwarfs, 2 QSOs, and 4 white dwarfs. Using the observed population of dwarfs with spectral type M4 or later, we derive a Galactic disk scale height of 400 \pm 100 pc for M and L stars. The local white dwarf density is computed to be as high as (1.1 \pm 0.3) x10^(-2) stars/pc^3. Based on observations taken 73 days apart, we determined that no object in the field has a proper motion larger than 0.027"/year (3 sigma detection limit). No high velocity white dwarfs were identified in the HUDF, and all four candidates appear more likely to be part of the Galactic thick disk. The lack of detected halo white dwarfs implies that, if the dark matter halo is 12 Gyr old, white dwarfs account for less than 10% of the dark matter halo mass.Comment: 35 pages, 11 figures, accepted by Ap

THE HUBBLE SPACE TELESCOPE WIDE FIELD CAMERA 3 EARLY RELEASE SCIENCE DATA: PANCHROMATIC FAINT OBJECT COUNTS FOR 0.2-2 μm WAVELENGTH

“…However, for objects at substantial redshifts (z 0.75-1), the SED will shift out of the UVIS sensitivity regime quickly enough to significantly reduce the red-leak. Hence, the WFC3 UVIS red-leaks in general only need to be corrected for the reddest (T eff 5000 K), lower- Malhotra et al 2005;Pirzkal et al 2004Pirzkal et al , 2005Pirzkal et al , 2009Straughn et al 2008Straughn et al , 2009) that reside inside the ERS mosaic are listed (see Figure 3). Note 2: the listed depth is the 50% completeness limit for 5σ detections in total SExtractor AB magnitudes for typical compact objects at this flux level (circular aperture with 0.…”

Morphology and Evolution of Emission‐Line Galaxies in the Hubble Ultra Deep Field

“…These images thus provide an excellent opportunity to measure the size and morphology of faint galaxies (M B P À18:0), extending previous studies to much lower luminosities. While the HUDF images do not provide spectroscopic redshifts of individual sources, the GRAPES program (Grism ACS Program for Extragalactic Science, PI: S. Malhotra; see description in Pirzkal et al 2004) yielded slitless spectroscopic observations of 1400 objects with i 775 27:0, or about 10% of the sources in the HUDF). We identified 124 objects (eGRAPES) with prominent emission lines (C. Xu et al 2006, in preparation).…”

“…First, eGRAPES were selected spectroscopically based on the presence of emission lines in their slitless spectra (Pirzkal et al 2004;C. Xu et al 2006, in preparation).…”

“…Sizes were measured using the same method described above in both the ACS B 435 -band image and the NICMOS J-band image. We first matched the resolution of the ACS B 435 -band image to the resolution of the NICMOS image using stars in the HUDF (Pirzkal et al 2005). We then computed the average ratio of sizes between the degraded ACS B-band image (i.e., 1500 8 rest frame) and the NICMOS J-band image (i.e., 4350 8 rest frame).…”

Star forming galaxies at z≈6 and reionization

“…It is interesting that the level of stellar contamination in the UDF i ′ -drops is only 2%, compared with about one in three at the bright end (z ′ AB < 25.6; Stanway, ). This may be because we are seeing through the Galactic disk at these faint limiting magnitudes to a regime where there are no stars (see also Pirzkal et al 2005). …”