The Phoenix Deep Survey: Extremely Red Galaxies and Cluster Candidates
Anthony G. Smith, Andrew M. Hopkins, Richard W. Hunstead, Samuel J. Schmidt, José Afonso, Antonis E. Georgakakis, Lawrence E. Cram, Bahram Mobasher, Mark Sullivan
We present the results of a study of a sample of 375 Extremely Red Galaxies (ERGs) in the Phoenix Deep Survey, 273 of which constitute a subsample which is 80% complete to K_s = 18.5 over an area of 1160 arcmin^2. The angular correlation function for ERGs is estimated, and the association of ERGs with faint radio sources explored. We find tentative evidence that ERGs and faint radio sources are associated at z > 0.5. A new overdensity-mapping algorithm has been used to characterize the ERG distribution, and identify a number of cluster candidates, including a likely cluster containing ERGs at 0.5 < z < 1. Our algorithm is also used in an attempt to probe the environments in which faint radio sources and ERGs are associated. We find limited evidence that the I - K_s > 4 criterion is more efficient than R - K_s > 5 at selecting dusty star-forming galaxies, rather than passively evolving ERGs.
The Phoenix Deep Survey (PDS) is a multiwavelength survey based on deep 1.4 GHz radio observations used to identify a large sample of star forming galaxies to z=1. Here we present an exploration of the evolutionary constraints on the star-forming population imposed by the 1.4 GHz source counts, followed by an analysis of the average properties of extremely red galaxies in the PDS, by using the "stacking" technique.
In this paper we explore the clustering properties and the environment of the Extremely Red Objects (EROs; I-K>4mag) detected in a ~180arcmin^2 deep (Ks~20mag) Ks-band survey of a region within the Phoenix Deep Survey, an on-going multiwavelength program aiming to investigate the nature and the evolution of faint radio sources. Using our complete sample of 289 EROs brighter than Ks=20mag we estimate a statistically significant (~3.7sigma) angular correlation function signal with amplitude Aw=8.7^{+2.1}_{-1.7}x10^{-3} consistent with earlier work based on smaller samples. This amplitude suggest…
Insensitive to dust obscuration, radio wavelengths are ideal to study star-forming galaxies free of dust induced biases. Using data from the Phoenix Deep Survey, we have identified a sample of star-forming extremely red objects (EROs). Stacking of the radio images of the radio-undetected star-forming EROs revealed a significant radio detection. Using the expected median redshift, we estimate an average star-formation rate of 61 M_sun/yr for these galaxies.
The Phoenix Deep Survey (PDS) is a multiwavelength survey based on deep 1.4 GHz radio observations used to identify a large sample of star forming galaxies to z=1. Photometric redshifts are estimated for the optical counterparts to the radio-detected galaxies, and their uncertainties quantified by comparison with spectroscopic redshift measurements. The photometric redshift estimates and associated best-fitting spectral energy distributions are used in a stacking analysis exploring the mean radio properties of U-band selected galaxies. Average flux densities of a few microJy are measured.
Due to their star formation history (SFH), the stellar population in Dwarf Galaxies (DG) is likely to have a metallicity spread which is best traced by the morphology of the Red Giant Branch (RGB). We probe here a purely empirical approach aimed at estimating average metallicity (Z) and Z spread by comparing the Color-Magnitude Diagrams (CMD) of galactic Globular Clusters (GCs) with those of two DGs: Leo A (HST data) and Phoe (VLT Fors2 data).
The Phoenix Deep Survey is a multi-wavelength galaxy survey based on deep 1.4 GHz radio imaging (Hopkins et al., 2003). The primary goal of this survey is to investigate the properties of star formation in galaxies and to trace the evolution in those properties to a redshift z=1, covering a significant fraction of the age of the Universe. By compiling a sample of star-forming galaxies based on selection at radio wavelengths we eliminate possible biases due to dust obscuration, a significant issue when selecting objects at optical and ultraviolet wavelengths. In this paper, we present the catal…
The initial Phoenix Deep Survey (PDS) observations with the Australia Telescope Compact Array have been supplemented by additional 1.4 GHz observations over the past few years. Here we present details of the construction of a new mosaic image covering an area of 4.56 square degrees, an investigation of the reliability of the source measurements, and the 1.4 GHz source counts for the compiled radio catalogue. The mosaic achieves a 1-sigma rms noise of 12 microJy at its most sensitive, and a homogeneous radio-selected catalogue of over 2000 sources reaching flux densities as faint as 60 microJy …
The Phoenix Deep Survey is a multi-wavelength survey based on deep 1.4 GHz radio imaging, reaching well into the sub-100 microJy level. One of the aims of this survey is to characterize the sub-mJy radio population, exploring its nature and evolution. In this paper we present the catalog and results of the spectroscopic observations aimed at characterizing the optically ``bright'' (R<~ 21.5 mag) counterparts of faint radio sources. Out of 371 sources with redshift determination, 21% have absorption lines only, 11% show AGN signatures, 32% are star-forming galaxies, 34% show narrow emission lin…
We estimate the star-formation rates and the stellar masses of the Extremely Red objects (EROs) detected in a 180arcmin2 Ks-band survey (Ks~20mag). This sample is complemented by sensitive 1.4GHz radio observations (12micro-Jy; 1sigma rms) and multiwaveband photometric data (UBVRIJ) as part of the Phoenix Deep Survey. For bright K<19.5mag EROs in this sample (I-K>4mag; total of 177) we use photometric methods to discriminate dust-enshrouded active systems from early-type galaxies and to constrain their redshifts. Radio stacking is then employed to estimate mean radio flux densities of 8.6 (3si…
Using a deep Australia Telescope Compact Array (ATCA) radio survey covering an area of ~3deg^{2} to a 4σsensitivity of \ge 100 \muJy at 1.4GHz, we study the nature of faint radio galaxies. About 50% of the detected radio sources are identified with an optical counterpart revealed by CCD photometry to m_{R}=22.5 mag. Near-infrared (K-band) data are also available for a selected sample of the radio sources, while spectroscopic observations have been carried out for about 40% of the optically identified sample. These provide redshifts and information on the stellar content. Emission-line ratios i…
In this paper we use a 50ks XMM-Newton pointing overlapping with the Phoenix Deep Survey, a homogeneous radio survey reaching muJy sensitivities, to explore the X-ray properties and the evolution of star-forming galaxies. UV, optical and NIR photometry is available and is used to estimate photometric redshifts and spectral types for radio sources brighter than R=21.5mag (total of 82). Sources with R<21.5mag and spiral galaxy SEDs (34) are grouped into two redshift bins with a median of z=0.240 and 0.455 respectively. Stacking analysis for both the 0.5-2 and 2-8keV bands is performed on these s…
We report on recent progress in the modelling of the near-IR spectra of young stellar populations, i.e. populations in which red supergiants (RSGs) are dominant. First, we discuss the determination of fundamental parameters of RSGs using fits to their near-IR spectra with new PHOENIX model spectra; RSG-specific surface abundances are accounted for and effects of the microturbulence parameter are explored. New population synthesis predictions are then described and, as an example, it is shown that the spectra of young star clusters in M82 can be reproduced very well from 0.5 to 2.4 micrometers.…
The nature of the extremely red galaxies is poorly known, the critical issue being whether they are old ellipticals at $z>1.5$ or distant star-forming galaxies strongly reddened by dust extinction. Here we review the little we know about them, and we present recent and preliminary results from our ongoing submillimeter -- millimeter observations.
We present the photometric redshift distribution of a sample of 198 Extremely Red Galaxies (ERGs) with Ks<22 and I-Ks>3.92 (Vega), selected by Roche et al. in 50.4 sq. arcmin of the Chandra Deep Field South (CDFS). The sample has been obtained using ISAAC-VLT and ACS-HST GOODS public data. We also show the results of a morphological study of the 72 brightest ERGs in the z band (z<25, AB).
We present a method based on two broad-band colors to investigate the nature of the Extremely Red Objects (EROs), i.e., the galaxies selected to have very red optical-to-infrared colors. Dusty starburst and old ellipticals at redshifts between 1 and 2 appear to occupy two different regions of the J-K vs. I-K color diagram, allowing for an easy classification. This diagnostic was applied to a complete sample of 57 EROs: the two populations are found to be present in the sample in similar abundances. The cosmic star formation density in the dusty starbursts is found to be of the order of that in…
Extremely Red Objects (EROs) provide the important possibility to shed light on the formation and evolution of the present-day massive ellipticals. On one hand, they allow to select z>1 old passively evolving spheroidals and to compare their abundance with the predictions of galaxy formation scenarios. On the other hand, they provide the possibility to find dust obscured starbursts, a fraction of which may trace the formation of proto-ellipticals at z>2. In this paper, the most recent results on EROs are reviewed and the main implications discussed.
We report observational analyses and theoretical interpretations of unusually red galaxies in the Subaru Deep Field (SDF). A careful analysis of the SDF data revealed a population with unusually red near-infrared (NIR) colors of J - K >~ 3-4, with higher confidence than the previous SDF result. Their surface number density drastically increases at K >~ 22 and becomes roughly the same with that of dusty starburst galaxies detected by submillimeter observations in recent years. These colors are even redder than the known population of the extremely red objects (EROs), and too red to explain by p…
We have discovered an excess of extremely red objects (EROs) surrounding the z=2.69 quasar QSO 1213-0017 (UM 485). Optical/IR colors for these galaxies are consistent with z=1-2 ellipticals, and there are at least 5 galaxies with spectroscopic redshifts at <z>=1.31. Keck optical spectra for 3 of the red galaxies show rest-frame UV breaks resembling local elliptical galaxies. Our initial results suggest a coherent structure in redshift, possibly arising from a massive galaxy cluster.
In the course of the follow-up multiwavelength study of a deep radio survey we have discovered that the milli-Jansky radio source PDFJ011423 is a low-redshift (z = 0.65) extremely red galaxy (ERG) with K=15.3, R-K = 5.8 and J-K = 3.1. Optical, infrared and radio photometry, together with optical and near-infrared spectroscopy, reveal a heavily obscured galaxy (A_V=5-6, from the observed Balmer decrement) undergoing vigorous star formation and presenting an active galactic nucleus (AGN). PDFJ011423 is a representative member of the dusty ERG population, providing a local counterpart for studyin…
At least half the radio galaxies at z>1 in the 7C Redshift Survey have extremely red colours (R-K>5), consistent with stellar populations which formed at high redshift (z>5). We discuss the implications of this for the evolution of massive galaxies in general and for the fraction of near-IR-selected EROs which host AGN, a result which is now being tested by deep, hard X-ray surveys. The conclusion is that many massive galaxies undergo at least two active phases: one at z~5 when the black hole and stellar bulge formed and another at z~1-2 when activity is triggered by an event such as an intera…
We present preliminary results of a 25 ks XMM-Newton observation of the largest sample of Extremely Red Objects (EROs) available to date (about 450 sources), selected in a contiguous area of 700 arcmin^2 (Daddi et al. 2000). Five of the 36 hard X-ray selected sources brighter than 7x10^{-15} erg cm^{-2} s^{-1} in the 2-10 keV band are associated with EROs. All of the X-ray detected EROs show rather extreme X-ray-to-optical flux ratios, suggesting the presence of highly obscured AGN activity.
We apply the Lyman absorption signature to search for galaxies at redshifts z \~ 6 - 17 using optical and infrared images of the Hubble Deep Field. The infrared images are sensitive to a point source 5 sigma detection threshold of AB(22,000) = 23.8, which adopting plausible assumptions to relate rest-frame ultraviolet flux densities to unobscured star formation rates is easily sufficient to detect the star formation rates expected for massive elliptical galaxy formation to quite high redshifts. For q_0 = 0.5, the infrared images are sensitive to an unobscured star formation rate of 100 h^-2 so…
We study 87 Extremely Red Objects (EROs), selected both to have color redder than R-[3.6] = 4.0, and to have confirmed spectroscopic redshifts. Together, these two constraints result in this sample populating a fairly narrow redshift range at 0.76 < z < 1.42. The key new ingredient included here is deep Spitzer Space Telescope InfraRed Array Camera (IRAC) data. Based on [3.6]-[8.0] color, we demonstrate that it is possible to classify EROs into early-type, dusty starburst, or power-law (AGN) types. We present ultraviolet to mid-infrared spectral energy distributions (SEDs) and Advanced Camera …
Preliminary results of a project aiming at unveiling the nature of the extremely red galaxies (ERGs) (objects with colours R-K>6 and I-K>5) found in deep optical-NIR surveys are presented. Very little is known about these objects, the critical issue being whether they are old ellipticals at z>1 or distant star-forming galaxies strongly reddened by dust extinction. We expect to shed light onto the unknown nature of these galaxies by completing our three-step project: (1) the construction of two very deep optical/NIR surveys to select ERGs, (2) subsequent VLT/NIR spectroscopy; (3) observations i…
We briefly discuss our survey of Extremely Red Objects (EROs) with HST/NICMOS and deep ground-based images and summarize its results. We use the high-resolution NICMOS images to sub-divide EROs into morphological classes, tentatively arguing that about 60 % of EROs (18 out of 30) are early-type galaxies. About 20 % (6 out of 30 objects) appear to be flattened disk systems. Another 10 % (3 out of 30) have an irregular morphology. Thus, combining disk and irregular systems, our data are compatible with 30 % of EROs being dusty starbursts. A small fraction (3 out of 30) appear point-like even on …
We have studied the spatial clustering of high redshift (z > 1) extremely red objects (EROs) as a function of photometric redshift in the GOODS Southern Field using public data. A remarkable overdensity of extremely red galaxies (I-Ks > 4) is found at an average photometric redshift z=1.10. Nine objects (six are EROs) within 50 arcsec of the brightest infrared galaxy in this overdensity present spectroscopic redshifts in the range 1.094 < z < 1.101 with a line-of-sight velocity dispersion of 433 km/s typical of an Abell richness class R=0 cluster. Other potential members of this cluster, desig…
We analyse whether hierarchical formation models based on Lambda cold dark matter cosmology can produce enough massive red galaxies to match observations. For this purpose, we compare with observations the predictions from two published models for the abundance and redshift distribution of Extremely Red Objects (EROs), which are red, massive galaxies observed at z >= 1. One of the models invokes a "superwind" to regulate star formation in massive haloes and the other suppresses cooling through "radio-mode" AGN feedback. The first one underestimates the number counts of EROs by an order of magn…
We present predictions for the abundance and nature of Extremely Red Objects (EROs) in the Lambda cold dark matter model. EROs are red, massive galaxies observed at z>= 1 and their numbers and properties pose a challenge to hierarchical galaxy formation models. We compare the predictions from two published models, one of which invokes a "superwind" to regulate star formation in massive haloes and the other which suppresses gas cooling in haloes through "radio-mode" AGN feedback. The superwind model underestimates the number counts of EROs by an order of magnitude, whereas the radio-mode AGN fe…
Extremely Red Objects (EROs, R-K>5) constitute a heterogenous class of extragalactic sources including high redshift elliptical galaxies, dusty star-forming systems and heavily obscured AGNs. Hard X-ray observations provide an unique and powerful tool to uncover obscured nuclear or star-forming activity. We present the results of XMM-Newton observations of the largest sample of EROs available to date (about 450 objects over a contiguous area of 700 arcmin^2). Five of the 46 hard X-ray selected sources brighter than 3x10^{-15} cgs in the 2-10 keV band, are associated with EROs. All of the X-ray…
We have performed a deep spectroscopic survey of extremely red galaxies on the GOODS-South field, using GMOS on Gemini South. We present here spectra and redshifts for 16 ERGs at 0.87<z<2.02, to a limit K=20.2. The ERHs are a mixture of spheroidals, mergers and spirals, with one AGN. For at least 10 of these galaxies we observe [OII] emission lines. We perform an age-dating analysis by fitting the spectra and 9-band photometry of the ERGs with models of passively evolving stellar populations combined with a younger star-forming component. The best-fitting ages for the old stellar components ra…
We present the preliminary results of Monte Carlo simulations aimed to investigate the effects of realistic dust extinction (absorption + scattering) on the colours of high-z galaxies. In this paper, we concentrate on the case of spheroidal galaxies, and we obtain attenuation curves in the range 0.1-1.2$μ$m for different dust spatial distributions, and for a range of values of the dust optical depth, geometrical thickness and inclination of the dust disk. We find that the resultant curves are strongly dependent on the dust geometrical distribution and optical depth. A serendipitous finding is …
Understanding the nature of Extremely Red Objects [EROs; (I-K)>=4] is one of the most challenging issues in observational cosmology. Here we report on the X-ray constraints provided by the 2 Ms Chandra Deep Field-North Survey (CDF-N). X-ray emission has been detected from 11 out of 36 EROs (approx 30%). Five of these have hard X-ray emission and appear to be obscured AGNs, while non-AGN emission (star formation or normal elliptical galaxy emission) is likely to be the dominant source of X-rays from the soft X-ray sources detected at the faintest X-ray flux levels.
We provide a high dispersion line-by-line abundance analysis of five red HB stars in the extremely metal rich galactic globular cluster NGC 6553. These red HB stars are significantly hotter than the very cool stars near the tip of the giant branch in such a metal rich globular cluster and hence their spectra are much more amenable to an abundance analysis than would be the case for red giants. We find that the mean [Fe/H] for NGC 6553 is -0.16 dex, comparable to the mean abundance in the galactic bulge found by McWilliam & Rich (1994) and considerably higher than that obtained from an analysis…
We present near-infrared VLT-UT1+ISAAC spectroscopy of a sample of 9 extremely red galaxies (ERGs) with R-K>5 and K<19.0. Neither strong emission lines (F_lim<1-5 10^{-16} erg s^{-1}cm^{-2}) nor continuum breaks are detected. From near-infrared spectrophotometry, complemented with broad-band optical and near-IR photometry, we estimate ``spectro-photometric'' redshifts to be in the range of 0.8<z_sphot<1.8. We derive upper limits on the star formation rates in range of SFR<6-30h_50^{-2} M_solar yr^{-1}. Two of the observed ERGs are dusty starburst candidates because they require strong dust red…
We present Spitzer Space Telescope observations of the well-studied extremely red objects (EROs) HR10 and LBDS53W091 from 3.6 to 160 microns. These galaxies are the prototypes of the two primary classes of EROs: dusty starbursts and old, evolved galaxies, respectively. Both galaxies, as well as LBDS53W069, another example of an old, quiescent galaxy, are well-detected out to 8 microns. However, only the dusty starburst HR10 is detected in the far-infrared. All three EROs have stellar masses of a few times 10^11 M(sun). Using evolutionary model fits to their multiband photometry, we predict the…
We report the first detection of the lowest CO transition in a sub-millimetre bright galaxy and extremely red object (ERO) at z = 1.44 using the Very Large Array. The total J = 1 - 0 line luminosity of ERO J164502+4626.4 is (7+-1) x 10^{10} K km s^{-1} pc^2, which yields a total molecular gas mass of ~6 x 10^{10} Msun. We also present a map of the 850-um continuum emission obtained using SCUBA, from which we infer a far-IR luminosity and dust mass of L_FIR ~ 9 x 10^{12} Lsun and M_d ~ 9 x 10^{8} Msun. We find tentative evidence that the CO and sub-mm dust emission is extended over several tens…
We present a catalog of extremely red objects discovered using the NICMOS/HST parallel imaging database and ground-based optical follow-up observations. Within an area of 16 square arc-minutes, we detect 15 objects with $\rm R - F160W > 5$ and $\rm F160W < 21.5$. We have also obtained K-band photometry for a subset of the 15 EROs. All of the $\rm R - F160W$ selected EROs imaged at K-band have $\rm R - K > 6$. Our objects have $\rm F110W - F160W$ colors in the range of 1.3 - 2.1, redder than the cluster ellipticals at $z \sim 0.8$ and nearly 1 magnitude redder than the average population select…
Near infrared imaging and spectroscopic observations of the extremely red object (R-K~ 7 mag) CL 0939+4713 B have been obtained with the Near Infrared Camera on the Keck I Telescope of the W. M. Keck Observatory. The imaging shows a slightly elongated structure, while the spectroscopy shows a continuum break that allows us to determine the redshift of z = 1.58 + 0.01/-0.03 for this system. The fits of a range of models to the infrared spectrum suggests that it is predominantly an old (> 10^9 yrs) stellar system that suffers little extinction, while the measurerd R and I magnitudes suggests an …
CO J = 5 - 4 and J = 2 - 1 emission lines were detected towards the extremely red galaxy (ERG) HR10 (J164502+4626.4) at z=1.44. The CO intensities imply a molecular gas mass M(H2) of 1.6 x 10^{11} h^{-2}_50 solar masses, and, combined with the intensity of the dust continuum, a gas-to-dust mass ratio around 200-400 (assuming galactic values for the conversion factors). The peak of the CO lines are at the same redshift as the [O II]3727 line, but blue- shifted by 430 km s^{-1} from the Halpha line. These CO detections confirm the previous results that HR10 is a highly obscured object with a lar…
We discuss the submillimeter properties of Extremely Red Objects (EROs) in the two Canada-UK Deep Submillimeter Survey (CUDSS) Fields. We measure the mean submillimeter flux of the ERO population (to K < 20.7) and find 0.4 +/- 0.07 mJy for EROs selected by (I-K) > 4.0 and 0.56 +/- 0.09 mJy for EROs selected by (R-K) > 5.3 but, these measurements are dominated by discrete, bright submillimeter sources. We estimate that EROs produce 7-11% of the far-infrared background at 850um. This is substantially less than a previous measurement by Wehner, Barger & Kneib (2002) and we discuss possible reason…
We present J band observations of a complete sample of 57 red galaxies selected to have K<20 and R-K>5.3. We use the Pozzetti and Mannucci (2000) prescriptions, based on the R-K and J-K colours, to separate the two dominant populations, old ellipticals and dusty starbursts. We find that both populations are present in the current sample and have similar abundances, and discuss the uncertainties in this result. Galactic stars comprise about 9% of the objects. The starburst galaxies of the present sample are found to give a contribution to the cosmic star formation density similar to the Lyman-b…
Infrared surveys have discovered a significant population of bright (K<19) extremely red (R-K>6) objects. Little is known about the properties of these objects on account of their optical faintness (R>24). Here, we report deep infrared imaging and spectroscopy of one of the extremely red objects (EROs) discovered by Hu \& Ridgway (1994) in the field of the z=3.79 quasar PC1643+4631A. The infrared images were obtained in 0.5" seeing, and show that the object (denoted HR10) is not a dynamically relaxed elliptical galaxy dominated by an old stellar population as was previously suspected, but inst…
We present a quantitative study of the morphology of 41 Extremely Red Objects (EROs). The analysis is based on deep otical and near-infrared images from the Hubble Space Telescope public archive, and performed by fitting to each galaxy image a PSF-convolved bi-dimensional model brightness distribution. Relying both on the visual inspection of the data and on the results of the fitting procedure, we are able to determine the fraction of irregular and/or interacting EROs, and to identify those that more closely resemble local ellipticals. To the former class, whose members are probably high-reds…
The radio emission during 201 X-ray selected solar flares was surveyed from 100 MHz to 4 GHz with the Phoenix-2 spectrometer of ETH Zurich. The selection includes all RHESSI flares larger than C5.0 jointly observed from launch until June 30, 2003. Detailed association rates of radio emission during X-ray flares are reported. In the decimeter wavelength range, type III bursts and the genuinely decimetric emissions (pulsations, continua, and narrowband spikes) were found equally frequently. Both occur predominantly in the peak phase of hard X-ray (HXR) emission, but are less in tune with HXRs th…
This paper presents infrared spectra taken with the newly commissioned NIRSPEC spectrograph on the Keck Telescope of the High Redshift Radio Galaxy MRC 2025-218 (z=2.630) and an extremely red galaxy (R-K > 6 mag) 9'' away. These observations represent the deepest infrared spectra of a radio galaxy to date and have allowed for the detection of Hbeta, OIII (4959/5007), OI (6300), Halpha, NII (6548/6583) and SII (6716/6713). The Halpha emission is very broad (FWHM~6000 km/s) and strongly supports AGN unification models linking radio galaxies and quasars. The line ratios are most consistent with a…
We use a serendipitously discovered overdensity of extremely red objects (EROs) to study the morphologies and cumulative surface number density of EROs in a dense environment. Our extremely deep imaging allows us to select very faint EROs, reaching Ks=21, or ~2 magnitudes fainter than the L* of passively evolving ellipticals at z=1.5. We find that the shape of the ERO cumulative surface number density in our overdense field mimics that of the field ERO population over all magnitudes down to Ks=21 but with a factor of 3-4 higher normalization. The excellent seeing in our images (0.4" in Ks and …
The colours of the galaxy class known as Extremely Red Objects (EROs; R-K>5) are considered to be consistent with two distinct galaxy populations at high redshift: evolved ellipticals or young dusty starbursts. In this paper the properties of EROs, spanned by the five photometric bands RIJHK, are investigated as to the possibility to distinguish between these two galaxy populations using only broad band photometry. The broad band colours of elliptical and starburst galaxies at redshifts up to 5 are computed from synthetic spectra obtained using the spectral evolution synthesis programme PEGASE…
We present fluorine abundances in seven red-giant members of the globular cluster M4 (NGC 6121). These abundances were derived from the HF (1--0) R9 line at 2.3357 microns in high-resolution infrared spectra obtained with the Phoenix spectrograph on Gemini-South. Many abundances in the target stars have been studied previously, so that their overall abundance distributions are well-mapped. The abundance of fluorine is found to vary by more than a factor of 6, with the F-19 variations being correlated with the already established oxygen variations, and anti-correlated with the sodium and alumin…
We present very long baseline interferometry (VLBI) images of ten very high redshift (z>3) quasars at 5 GHz. The sources 0004+139, 0830+101, 0906+041, 0938+119 and 1500+045 were observed in September 1992 using a global VLBI array, while 0046+063, 0243+181, 1338+381, 1428+423 and 1557+032 were observed in October 1996 with the European VLBI Network and Hartebeesthoek, South Africa. Most of the sources are resolved and show asymmetric structure. The sample includes 1428+423, the most distant radio loud quasar known to date (z=4.72). It is barely resolved with an angular resolution of about 2.0*…
We have mapped the submillimetre wavelength continuum emission from the Subaru Deep Field (SDF) at 450 and 850 microns with the Submillimetre Common-User Bolometer Array (SCUBA) detector on the James Clerk Maxwell Telescope (JCMT). The near-IR image of the SDF is one of the deepest near-IR images available and contains four `hyper extremely red objects' (HEROs). These data allow us to test the connection between `extremely red objects' (EROs) found in IR surveys and the population of bright submillimetre sources found with SCUBA. We present a weak measurement of the average flux of the four K-…
We analyze the X-ray properties of a near-infrared selected (Ks < 20) sample of spectroscopically identified Extremely Red Objects (R-Ks>5) in a region of the Chandra Deep Field-South using the public 1 Ms observation. The 21 objects were classified, on the basis of deep VLT spectra, in two categories: 13 dusty star-forming galaxies showing [OII] emission, and 8 early-type galaxies with absorption features in their optical spectra. Only one emission line object has been individually detected; its very hard X-ray spectrum and the high intrinsic X-ray luminosity unambiguously reveal the presence…
We have serendipitously discovered an extremely lithium-rich star on the red giant branch of the globular cluster M3 (NGC 5272). An echelle spectrum obtained with the Keck I HIRES reveals a Li I 6707 Angstrom resonance doublet of 520 milli-Angstrom equivalent width, and our analysis places the star among the most Li-rich giants known: log[epsilon(Li)] ~= +3.0. We determine the elemental abundances of this star, IV-101, and three other cluster members of similar luminosity and color, and conclude that IV-101 has abundance ratios typical of giants in M3 and M13 that have undergone significant mi…
The extremely red galaxies (ERGs) are defined in terms of their very red optical-to-near IR colours (as R-K>5 or I-K>4). Originally this selection was aimed at selecting old (> 1 Gyr) passively evolving elliptical galaxies at intermediate redshift (1<z<2), but it was soon discovered that young star-forming dusty galaxies can show similar colours and therefore be selected in the same surveys. It is crucial to distinguish between these two populations because they have very different consequences on the models of galaxy formation. Here we show that old ellipticals and dusty starburst are expecte…
We present initial results from a field survey for extremely red objects (EROs, defined here as (R-K') >= 6 mag) covering 154 square arcminutes of sky, from the first of 7 deep, wide-field K' images obtained as part of the Calar Alto Deep Imaging Survey (CADIS). The 5-sigma point source detection limits are K'=20.5 and R=25.0, while extended-source limits are up to 0.5-0.75 mag brighter. We identify a total of 8 bright EROs with K' =< 19.0. Six of these bright EROs are resolved and are likely to be galaxies, while the remaining 2 are unresolved, with colors consistent with their being low-mass…
Extremely Red Objects (EROs) offer a window to the universe at z~1 analogous to that provided by the Lyman Break galaxies at z=3. Passive evolution and hierarchical galaxy formation models make very distinct predictions for the K (2.2um) surface density of galaxies at z~1 and EROs are a powerful constraint on these theories. I present a study of nine resolved EROs with R-K>5.3 and K<18 mag found in the 185 arcmin^2 of the Deep Multicolor Survey with near-infrared imaging. Photometric redshifts for these galaxies shows they all lie at z=0.8-1.3. The relatively blue J-K colors of these galaxies …
We present the results of a K-band imaging survey of 40 arcmin^{2} in fields around 14 radio-loud AGN (6 radio galaxies and 8 quasars) with z>1.5. The survey, 80% complete to K<19.2 and complemented by R-band imaging, aimed at investigating whether extremely red objects (EROs) are present in excess around high-z AGN, and to study the environment of z>1.5 radio galaxies and radio-loud quasars. At $18<K<19$ the differential galaxy counts in our fields suggest a systematic excess over the general field counts. At K<19.2, we find an excess of galaxies with R-K>6 compared to the general field. Cons…
The extremely red colors of some transneptunian objects and Centaurs are not seen among the Jupiter family comets which supposedly derive from them. Could this mismatch result from sublimation loss of colorless ice? Radiative transfer models show that mixtures of volatile ice and nonvolatile organics could be extremely red, but become progressively darker and less red as the ice sublimates away.
We report the redshift measurement for the submillimeter selected galaxy SMMJ04431+0210 (N4) using the Near Infrared Spectrograph on the Keck-II telescope. The data show H-alpha, [NII]6583,6548, and [OIII]5007 lines at a redshift of z=2.51. The high nuclear [NII]/H-alpha line ratio is consistent with a LINER or Type-II AGN. The H-alpha emission is spatially resolved, suggesting the presence of significant star-forming activity outside the nucleus. From imaging with the Near Infrared Camera on the Keck-I telescope, we find an extremely red near-infrared color of J-K=3.2 for N4. Follow-up redshi…
We report the serendipitous discovery of an extremely red object in the Hubble Deep Field South (HDFS) Test NICMOS (Near Infrared Camera and Multi Object Spectrograph) field of view. The object is resolved in the NICMOS image and has a light profile very well described by an r^{1/4} law with effective radius r_e=0."20+-0."05 and H_{AB}=21.7+-0.1 magnitudes. In contrast, the galaxy is undetected in the R and I band ground based images taken at the CTIO 4 m Blanco Telescope, giving a lower limit to the color of (R-H)_{AB}>3.9 and (I-H)_{AB}>3.5 at the 95% confidence level. The colors of a range …
We construct a sample of extremely red objects (EROs) within the UKIDSS Ultra Deep Survey by combining the Early Data Release with optical data from the Subaru/XMM-Newton Deep Field. We find a total of 3715 objects over 2013 sq. arcmin with R-K>5.3 and K<=20.3, which is a higher surface density than found by previous studies. This is partly due to our ability to use a small aperture in which to measure colours, but is also the result of a genuine overdensity of objects compared to other fields. We separate our sample into passively-evolving and dusty star-forming galaxies using their RJK colou…
