Radio and X-ray properties of submillimeter galaxies in the A2125 field

We present the radio and X-ray properties of 1.2 mm MAMBO source candidates in a 1600 sq. arcmin field centered on the Abell 2125 galaxy cluster at z=0.247. The brightest, non-synchrotron mm source candidate in the field has a photometric redshift, z = 3.93^+1.11_-0.80, and is not detected in a 31 ks Chandra X-ray exposure. These findings are consistent with this object being an extremely dusty and luminous starburst galaxy at high-redshift, possibly the most luminous yet identified in any blank-field mm survey. The deep 1.4 GHz VLA imaging identifies counterparts for 83% of the 29 mm source candidates identified at >=4-sigma S(1.2mm) = 2.7 - 52.1 mJy, implying that the majority of these objects are likely to lie at z <~ 3.5. The median mm-to-radio wavelength photometric redshift of this radio-detected sample is z~2.2 (first and third quartiles of 1.7 and 3.0), consistent with the median redshift derived from optical spectroscopic surveys of the radio-detected subsample of bright submm galaxies (S(850um) > 5 mJy). Three mm-selected quasars are confirmed to be X-ray luminous in the high resolution Chandra imaging, while another mm source candidate with potential multiple radio counterparts is also detected in the X-ray regime. Both of these radio counterparts are positionally consistent with the mm source candidate. One counterpart is associated with an elliptical galaxy at z = 0.2425, but we believe that a second counterpart associated with a fainter optical source likely gives rise to the mm emission at z~1.Comment: Accepted for publication in Ap

Coordinated thermal and optical observations of Trans-Neptunian object (20000) Varuna from Sierra Nevada

We report on coordinated thermal and optical measurements of trans-Neptunian object (20000) Varuna obtained in January-February 2002, respectively from the IRAM 30-m and IAA 1.5 m telescopes. The optical data show a lightcurve with a period of 3.176+/-0.010 hr, a mean V magnitude of 20.37+/-0.08 and a 0.42+/-0.01 magnitude amplitude. They also tentatively indicate that the lightcurve is asymmetric and double-peaked. The thermal observations indicate a 1.12+/-0.41 mJy flux, averaged over the object's rotation. Combining the two datasets, we infer that Varuna has a mean 1060(+180/-220) km diameter and a mean 0.038(+0.022/-0.010) V geometric albedo, in general agreement with an earlier determination using the same technique.Comment: Accepted for publication in Astronomy & Astrophysics (7 pages, including 3 figures

Continuum millimetre observations of high-redshift radio-quiet QSOs. II. Five new detections at z > 4

We have performed a sensitive (σ ~ 1.5mJy) systematic study of the 1.25 mm emission of ~22 radio-quiet QSOs at z ≳ 4, with the IRAM 30m telescope equipped with bolometer arrays. Five radio-quiet QSOs at z > 4 have been detected at a 5-σ level in addition to the initial detection of the z = 4.7 QSO BR1202-0725 reported in McMahon et al. (1994). The detected fluxes range from 2.5 to 10 mJy. All the reported detections were independently confirmed at the 3-σ level on at least three different nights. In addition 10 other QSOs from the Cambridge APM survey sample and 6 others QSOs from the literature were searched for millimetre emission but not detected with 2-σ upper limits of 3-4 mJy. From this systematic study of about half of the known optically selected z > 4 QSOs, some general trends of their millimetre emission can be inferred. All the QSOs we have detected pertain to the APM sample and are among those which have the largest UV rest-frame luminosities. The detection rate within the APM sample is 6 out of 16 observed, compared with zero in the remaining 6. Two of the four APM broad absorption line QSOs observed were detected and four of the seven weak lined APM QSOs were detected, whereas none of the five strong lined APM QSOs were detected. Thus there is evidence for enhanced millimetre emission from luminous QSOs with weak broad emission lines or broad absorption lines. There is one clear case known of strong lensing amongst the six millimetre detected objects with z > 4. In light of the fact that both previously known objects with confirmed strong millimetre emission at z>2 are gravitationally lensed, i.e. H1413+ 117 and IRAS F10214+4724, sensitive high resolution observations of these z > 4 QSOs are required to determine whether gravitational lensing effects need to be taken into account. Assuming that the millimetre wave continuum emission is due to dust emission, the very large amount of dust implied, ~ 10^8 h^(-2) M_⊙ , means that the host galaxies of these QSOs have undergone a substantial phase of star formation. If the gas-to-dust ratio in these galaxies is similar to that in lower redshift objects, the total gas mass would be ~ 10^(11) M_⊙. We have begun to explore the 1.25 mm emission of bright radio-quiet QSOs in the redshift range 1.5 to 3.5, using criteria which seem to favor millimetre detections, established from our z > 4 detections. One source was detected at z = 2.70. We have also observed three QSOs with z > 3 that were previously studied at 1.25mm by Andreani et al. (1993) who reported detections at a level higher than 3σ. We have been unable to confirm any of these reported detections. In particular we have a 3σ upper limit of 3.2 mJy for the z = 3.19 QSO PC2132+0126 for which Andreani et al. reported a flux of 11.5 ± 1. 7 mJy. Either this source has substantially varied during the period between the two sets of observations or the single channel bolometer observations were affected by systematic errors

Dust emission from the lensed Lyman break galaxy cB58

We detect 1.2mm continuum emission from dust in the gravitationally lensed Lyman break galaxy MS 1512+36-cB58. Our detected flux is surprisingly low: relative to local starburst galaxies, cB58 appears to produce somewhat less far-IR emission than its UV reddening predicts. After comparing several different estimates of the source's dust content, we conclude that the apparent discrepancy is most likely related to uncertainty in its UV spectral slope. Alternate scenarios to account for a far-IR "deficit" which rely on a high dust temperature or differential magnification are less satisfactory. Our result underscores one of the risks inherent in characterizing the cosmic star formation history from rest-UV data alone.Comment: 5 pages, 1 figure, accepted by A&A Letter

Scanning tunneling microscopy of amorphous alloy electrocatalysts for water electrolysis

The surface topography of amorphous metals useful as electrocatalysts in water electrolysis, denoted as G16 (Cos50Ni25Si15Bu10) and G14 (Fe60Co20Si10B10), are studied at the gm scale with a conventional SEM, and at the nm scale with the STM. Both untreated specimens as well as those employed as electrodes for a relatively prolonged time exhibit the same microstructure with amorphous and crystalline surface regions. The microcrystallite reduced size structure, probably involving a very compact structure, appears to be of the greatest importance concerning the electrocatalytic activity of these materials.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

COSBO: The MAMBO 1.2 Millimeter Imaging Survey of the COSMOS Field

The inner 20 × 20 arcmin^2 of the COSMOS field was imaged at 250 GHz (1.2 mm) to an rms noise level of ~1 mJy per 11" beam using the Max-Planck Millimeter Bolometer Array (MAMBO-2) at the IRAM 30 m telescope. We detect 15 sources at significance between 4 and 7 σ, 11 of which are also detected at 1.4 GHz with the VLA with a flux density >24 μJy (3 σ). We identify 12 more lower significance mm sources based on their association with faint radio sources. We present the multifrequency identifications of the MAMBO sources, including VLA radio flux densities, optical and near-infrared identifications, as well as the XMM-Newton X-ray detection for two of the mm sources. We compare radio and optical photometric redshifts and briefly describe the host galaxy morphologies. The colors of the identified optical counterparts suggest most of them to be high-redshift (z ~ 2-3) star-forming galaxies. At least three sources appear lensed by a foreground galaxy. We highlight some MAMBO sources that do not show obvious radio counterparts. These sources could be dusty starburst galaxies at redshifts >3.5. The 250 GHz source areal density in the COSMOS field is comparable to that seen in other deep mm fields

MITO measurements of the Sunyaev-Zeldovich Effect in the Coma cluster of galaxies

We have measured the Sunyaev-Zeldovich effect towards the Coma cluster (A1656) with the MITO experiment, a 2.6-m telescope equipped with a 4-channel 17 arcminute (FWHM) photometer. Measurements at frequency bands 143+/-15, 214+/-15, 272+/-16 and 353+/-13 GHz, were made during 120 drift scans of Coma. We describe the observations and data analysis that involved extraction of the S-Z signal by employing a spatial and spectral de-correlation scheme to remove a dominant atmospheric component. The deduced values of the thermal S-Z effect in the first three bands are DT_{0} = -179+/-38,-33+/-81,170+/-35 microKelvin in the cluster center. The corresponding optical depth, tau=(4.1+/-0.9) 10^{-3}, is consistent (within errors) with both the value from a previous low frequency S-Z measurement, and the value predicted from the X-ray deduced gas parameters.Comment: Ap.J.Letters accepted, 4 pages, 2 figure

Discovery of an extremely bright submillimeter galaxy at z=3.93

Serendipitously we have discovered a rare, bright submillimeter galaxy (SMG) with a flux density of 30 +/- 2 mJy at lambda=1.2mm, using MAMBO2 at the IRAM 30-meter millimeter telescope. Although no optical counterpart is known for MM18423+5938, we were able to measure the redshift z=3.92960 +/- 0.00013 from the detection of CO lines using the IRAM Eight MIxer Receiver (EMIR). In addition, by collecting all available photometric data in the far-infrared and radio to constrain its spectral energy distribution, we derive the FIR luminosity 4.8 10^14/m Lsol and mass 6.0 10^9/m Msol for its dust, allowing for a magnification factor m caused by a probable gravitational lens. The corresponding star-formation rate is 8.3 10^4/m Msol/yr. The detection of three lines of the CO rotational ladder, and a significant upper limit for a fourth CO line, allow us to estimate an H2 mass of between 1.9 10^11/m Msol and 1.1 10^12/m Msol. The two lines CI(3p1-3p0) and CI(3p2-3p1) were clearly detected and yield a [CI]/[H2] number abundance between 1.4 10^-5 and 8.0 10^-5. Upper limits are presented for emission lines of HCN, HCO^+, HNC, H_2O and other molecules observed. The moderate excitation of the CO lines is indicative of an extended starburst, and excludes the dominance of an AGN in heating this high-redshift SMG.Comment: Model revised. Accepted as an Astronomy and Astrophysics Letter, 4 pages, 3 figure

Vigorous star formation hidden by dust in a galaxy at z=1.4z=1.4

Near-infrared surveys have revealed a substantial population of enigmatic faint galaxies with extremely red optical-to-near-infrared colours and with a sky surface density comparable to that of faint quasars. There are two scenarios for these extreme colours: (i) these distant galaxies have formed virtually all their stars at very high redshifts and, due to the absence of recently formed stars, the colours are extremely red and (ii) these distant galaxies contain large amounts of dust, severely reddening the rest-frame UV--optical spectrum. HR10 ($z = 1.44$) is considered the archetype of the extremely red galaxies. Here we report the detection of the continuum emission from HR10 at 850$\mu$m and at 1250$\mu$m, demonstrating that HR10 is a very dusty galaxy undergoing a major episode of star formation. Our result provides a clear example of a high-redshift galaxy where the star formation rate inferred from the ultraviolet luminosity would be underestimated by a factor up to 1000, and shows that great caution should be used to infer the global star formation history of the Universe from optical observations only.Comment: 12 pages, 1 figure, Nature, in press (30 April 1998