اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدSpectra of High Redshift Galaxies using a Cluster as a Gravitational Telescope
65
0
0.0
(
0
)
تأليف
D. Mehlert
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Using the Focal Reducer Spectrograph (FORS) at the Very Large Telescope (VLT) during the FORS commissioning time in December 1998 we took long slit spectra of the gravitational arc visible on images of the galaxy cluster 1E 0657 (z = 0.296). This cluster is one of the hottest (massive) cluster known so far and hence perfectly acts as a gravitational telescope magnifying the flux of background sources up to a factor of 17. Here we present the spectra of the gravitational arc (z = 3.23) and 4 additional high redshift objects (z=2.35 to 3.09), that also fall on the slit by chance coincidence. We briefly discuss the stellar contents of these galaxies and show first models of the observed spectra. Furthermore we point out the effectivity of using FORS in combination with available gravitational telescopes.
قيم البحث
اقرأ أيضاً
Using a combination of near-infrared and optical photometry, along with multi-object spectroscopy, we have confirmed the existence of a high-redshift cluster of galxies at z = 0.96. The cluster was found using a wide-angle tailed radio source selecte
d from the VLA FIRST survey as a cluster signpost. These types of radio sources are often found in clusters, and are thought to attain their C-shaped morphologies from the relative motion between the radio source host galaxy and the intracluster medium. We present optical/near-infrared color-magnitude diagrams which show a concentration of cluster galaxies in color space. We also include spectroscopic results obtained from the Keck II LRIS. Ten galaxies are confirmed at the cluster redshift, with a line-of-sight velocity dispersion of 530 +190/-90 km/s, typical of an Abell richness class 0 cluster. Using data from the ROSAT public archive, we limit the X-ray luminosity for the cluster to less than 3 x 10^{44} erg/s, consistent with the value expected from the L_X - sigma relation.
We investigate the region around the Planck-detected z=3.26 gravitationally lensed galaxy HATLAS J114637.9-001132 (hereinafter HATLAS12-00) using both archival Herschel data from the H-ATLAS survey and using submm data obtained with both LABOCA and S
CUBA2. The lensed source is found to be surrounded by a strong overdensity of both Herschel-SPIRE sources and submm sources. We detect 17 bright (S_870 >~7 mJy) sources at >4sigma closer than 5 arcmin to the lensed object at 850/870 microns. Ten of these sources have good cross-identifications with objects detected by Herschel-SPIRE which have redder colours than other sources in the field, with 350 micron flux > 250 micron flux, suggesting that they lie at high redshift. Submillimeter Array (SMA) observations localise one of these companions to ~1 arcsecond, allowing unambiguous cross identification with a 3.6 and 4.5 micron Spitzer source. The optical/near-IR spectral energy distribution (SED) of this source is measured by further observations and found to be consistent with z>2, but incompatible with lower redshifts. We conclude that this system may be a galaxy cluster/protocluster or larger scale structure that contains a number of galaxies undergoing starbursts at the same time.
We use the semi-analytic models of galaxy formation developed by Kauffmann, White & Guiderdoni to generate predictions for the observed properties of cluster and group galaxies at redshifts between 0 and 0.6. We examine four sets of cosmological init
ial conditions: low-density CDM models with and without cosmological constant, a flat CDM model and a mixed dark matter model. These models were selected because they span a wide range in cluster formation epoch. The semi-analytic models that we employ are able to follow both the evolution of the dark matter component of clusters and the formation and evolution of the stellar populations of the cluster galaxies. We are thus able to generate model predictions that can be compared directly with the observational data. In the low-density CDM models, clusters form at high red- shift and accrete very little mass at recent times. Our models predict that essentially no evolution in the observed properties of clusters will have occurred by a redshift of 0.6, in direct contradiction with the data. In contrast, in the MDM model, both galaxies and clusters form extremely late. This model predicts evolution which appears to be too extreme to be in agreement with the observations. The flat CDM model, which is intermediate in structure formation epoch, is most successful. This model is able to account for the evolution of the blue fraction of rich clusters with redshift, the relationship between blue fraction and cluster richness at different epochs, and the changes in the distribution of the morphologies of cluster galaxies by a redshift of 0.4.
We compare the relations among various integrated characteristics of ~25,000 low-redshift (z<1.0) compact star-forming galaxies (CSFGs) from Data Release 16 (DR16) of the Sloan Digital Sky Survey (SDSS) and of high-redshift (z>1.5) star-forming galax
ies (SFGs) with respect to oxygen abundances, stellar masses M*, far-UV absolute magnitudes M(FUV), star-formation rates SFR and specific star-formation rates sSFR, Lyman-continuum photon production efficiencies (xi_ion), UV continuum slopes beta, [OIII]5007/[OII]3727 and [NeIII]3868/[OII]3727 ratios, and emission-line equivalent widths EW([OII]3727), EW([OIII]5007), and EW(Halpha). We find that the relations for low-z CSFGs with high equivalent widths of the Hbeta emission line, EW(Hbeta)>100A, and high-z SFGs are very similar, implying close physical properties in these two categories of galaxies. Thus, CSFGs are likely excellent proxies for the SFGs in the high-z Universe. They also extend to galaxies with lower stellar masses, down to ~10^6 Msun, and to absolute FUV magnitudes as faint as -14 mag. Thanks to their proximity, CSFGs can be studied in much greater detail than distant SFGs. Therefore, the relations between the integrated characteristics of the large sample of CSFGs studied here can prove very useful for our understanding of high-z dwarf galaxies in future observations with large ground-based and space telescopes.
We present the first mid-infrared Spitzer/Infrared Spectrograph (IRS) observations of powerful radio galaxies at z>2. These radio galaxies, 4C +23.56 (z=2.48) and 6C J1908+7220 (z=3.53), both show strong mid-infrared continua, but with 6C J1908+7220
also showing strong PAH emission at rest-frame 6.2 and 7.7um. In 4C+23.56 we see no obvious PAH features above the continuum. The PAH emission in 6C J1908+7220 is the amongst the most distant observed to date and implies that there is a large instantaneous star formation rate (SFR). This is consistent with the strong detection of 6C J1908+7220 at far-IR and sub-mm wavelengths, indicative of large amounts of cold dust, ~10^9Msun. Powerful radio galaxies at lower redshifts tend to have weak or undetectable PAH features and typically have lower far-IR luminosities. In addition, 4C 23.56 shows moderate silicate absorption as seen in less luminous radio galaxies, indicating tau_{9.7um}=0.3+/-0.05. This feature is shifted out of the observed wavelength range for 6C J1908+7220. The correlation of strong PAH features with large amounts of cold dust, despite the presence of a powerful AGN, is in agreement with other recent results and implies that star formation at high redshift is, in some cases at least, associated with powerful, obscured AGN.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
