目录
图像
上传图像
DSS Images Other Images
相关文章
Using Resolved Galaxies in Hubble Space Telescope Images to Measure Absolute Proper Motions
We explore the possibility of using resolved background galaxies tomeasure accurate absolute proper motions with the Hubble SpaceTelescope. Because galaxies are not point sources, we cannot usestellar point-spread functions (PSFs) to measure their positions.Rather, we must develop a template for each galaxy that can be used tomeasure a consistent position for it in each exposure at each epoch. Wefind that there are enough measurable galaxies in a 1200-s exposure inF606W and F775W to define an astrometric reference frame to better than0.02 WFC pixel (1 mas). There are, however, some limitations. Forexample, observations taken at different orientations may suffer fromthe fact that the PSF is asymmetric, which can induce apparent shifts inthe positions of stars and galaxies when the field is rotated relativeto the PSF. This is present at the 0.03-pixel level. Nonetheless, beingable to measure absolute proper motions relative to background galaxieswill open up some interesting possibilities for targeted observationsand pencil-beam surveys. This investigation uses the Ultra Deep Field,but the concept could work for any deep field that has extragalacticsources and dithered observations.
| Galaxies in the Hubble Ultra Deep Field. I. Detection, Multiband Photometry, Photometric Redshifts, and Morphology
We present aperture-matched point-spread function (PSF)-correctedBVi'z'JH photometry and Bayesian photometric redshifts (BPZ) for objectsdetected in the Hubble Ultra Deep Field (UDF), 8042 of which aredetected at the 10 σ level (e.g., i'<29.01 orz'<28.43). Most of our objects are defined identically tothose in the public STScI catalogs, enabling a straightforwardobject-by-object comparison. We have combined detections from i', z',J+H, and B+V+i'+z' images into a singlecomprehensive segmentation map. Using a new program called SExSeg, weare able to force this segmentation map into SExtractor for photometricanalysis. The resulting photometry is corrected for the wider NIC3 PSFsusing our ColorPro software. We also correct for the ACS z'-band PSFhalo. Offsets are applied to our NIC3 magnitudes, which are found to betoo faint relative to the ACS fluxes. Based on BPZ spectral energydistribution (SED) fits to objects of known spectroscopic redshift, wederived corrections of -0.30+/-0.03 mag in J and -0.18+/-0.04 mag in H.Our offsets appear to be supported by a recent recalibration of the UDFNIC3 images combined with nonlinearity measured in NICMOS itself. TheUDF reveals a large population of faint blue galaxies (presumably youngstarbursts), bluer than those observed in the original Hubble DeepFields. To accommodate these galaxies, we have added two new starbursttemplates to the SED library used in previous BPZ papers. The resultingphotometric redshifts are accurate to within 0.04(1+zspec)out to z<6. Our BPZ results include a full redshift probabilitydistribution for each galaxy. By adding these distributions, we obtainthe redshift probability histogram for galaxies in the UDF. Medianredshifts are also provided for different magnitude-limited samples.Finally, we measure galaxy morphology, including Sérsic index andasymmetry. Simulations allow us to quantify the reliability of ourmorphological results. Our full catalog, along with our softwarepackages SExSeg and ColorPro, is available from our ACS Web site.
| ESO imaging survey: infrared observations of CDF-S and HDF-S
This paper presents infrared data obtained from observations carried outat the ESO 3.5 m New Technology Telescope (NTT) of the Hubble Deep FieldSouth (HDF-S) and the Chandra Deep Field South (CDF-S). These data weretaken as part of the ESO Imaging Survey (EIS) program, a public surveyconducted by ESO to promote follow-up observations with the VLT. In theHDF-S field the infrared observations cover an area of ~53 squarearcmin, encompassing the HST WFPC2 and STIS fields, in theJHKs passbands. The seeing measured in the final stackedimages ranges from 0.79 arcsec to 1.22 arcsec and the median limitingmagnitudes (AB system, 2'' aperture, 5σ detection limit) areJ_AB˜23.0, H_AB˜22.8 and K_AB˜23.0 mag. Less completedata are also available in JKs for the adjacent HST NICMOSfield. For CDF-S, the infrared observations cover a total area of ~100square arcmin, reaching median limiting magnitudes (as defined above) ofJ_AB˜23.6 and K_AB˜22.7 mag. For one CDF-S field H band dataare also available. This paper describes the observations and presentsthe results of new reductions carried out entirely through theun-supervised, high-throughput EIS Data Reduction System and itsassociated EIS/MVM C++-based image processing library developed, overthe past 5 years, by the EIS project and now publicly available. Thepaper also presents source catalogs extracted from the final co-addedimages which are used to evaluate the scientific quality of the surveyproducts, and hence the performance of the software. This is donecomparing the results obtained in the present work with those obtainedby other authors from independent data and/or reductions carried outwith different software packages and techniques. The final science-gradecatalogs together with the astrometrically and photometricallycalibrated co-added images are available at CDS.
| The Near-Infrared Camera and Multi-Object Spectrometer Ultra Deep Field: Observations, Data Reduction, and Galaxy Photometry
This paper describes the observations and data reduction techniques forthe version 2.0 images and catalog of the Near-Infrared Camera andMulti-Object Spectrometer Ultra Deep Field (NICMOS UDF) Treasuryprogram. All sources discussed in this paper are based on detections inthe combined NICMOS F110W and F160W bands only. The NICMOS images aredrizzled to 0.09" pixel-1 and aligned to the Advanced Camerafor Surveys UDF F850LP image, which was rebinned to the same pixelscale. These form the NICMOS version 2.0 UDF images. The catalog sourcesare chosen with a conservative detection limit to avoid the inclusion ofnumerous spurious sources. The catalog contains 1293 objects in the144''×144'' NICMOS subfield of the UDF. The5 σ signal-to-noise ratio level is an average 0.6" diameteraperture AB magnitude of 27.7 at 1.1 and 1.6 μm. The catalog sources,listed in order of right ascension, satisfy a minimum signal-to-noiseratio criterion of 1.4 σ in at least seven contiguous pixels ofthe combined F110W and F160W image.
| Stars in the Hubble Ultra Deep Field
We identified 46 unresolved source candidates in the Hubble Ultra DeepField (HUDF) down to i775=29.5. Unresolved objects wereidentified using a parameter S, which measures the deviation from thecurve of growth of a point source. Extensive testing of this parameterwas carried out, including the effects of decreasing signal-to-noiseratio and of the apparent motions of stars, which demonstrated thatstars brighter than i775=27.0 could be robustly identified.Low-resolution grism spectra of the 28 objects brighter thani775=27.0 identify 18 M and later stellar type dwarfs, twocandidate L dwarfs, two QSOs, and four white dwarfs. Using the observedpopulation of dwarfs with spectral type M4 or later, we derive aGalactic disk scale height of 400+/-100 pc for M and L stars. The localwhite dwarf density is computed to be as high as(1.1+/-0.3)×10-2 stars pc-3. On the basis ofobservations taken 73 days apart, we determined that no object in thefield has a proper motion larger than 0.027" yr-1 (3 σdetection limit). No high-velocity white dwarfs were identified in theHUDF, and all four candidates appear more likely to be part of theGalactic thick disk. The lack of detected halo white dwarfs implies thatif the dark matter halo is 12 Gyr old, white dwarfs account for lessthan 10% of the dark matter halo mass.
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
