C. J. Salter
University of Puerto Rico at Arecibo, Arecibo, Arecibo, Puerto Rico

Are you C. J. Salter?

Claim your profile

Publications (36)58.18 Total impact

  • Article: Radio polarimetry of compact steep spectrum sources at sub-arcsecond resolution
    F. Mantovani, A. Rossetti, W. Junor, D. J. Saikia, C. J. Salter
    [show abstract] [hide abstract]
    ABSTRACT: Aims - We report new Very Large Array polarimetric observations of Compact Steep-Spectrum (CSS) sources at 8.4, 15, and 23GHz. Methods - Using multi-frequency VLA observations we have derived sub-arcsecond resolution images of the total intensity, polarisation, and rotation measure (RM) distributions. Results heading - We present multi-frequency VLA polarisation observations of CSS sources. About half of the sources are point-like even at the resolution of about 0.1x0.1 arcseconds. The remaining sources have double or triple structure. Low values for the percentage of polarised emission in CSS sources is confirmed. On the average, quasars are more polarised than galaxies. A wide range of RM values have been measured. There are clear indications of very large RMs up to 5\,585 rad m**(-2). CSS galaxies are characterized by RM values that are larger than CSS quasars. The majority of the objects show very large values of RM. Conclusions - The available data on sub-arcsecond-scale rest-frame RM estimates for CSS sources show that these have a wide range of values extending up to about 36,000 rad m**(-2). RM estimates indicate an overall density of the magneto-ionic medium larger than classical radio sources.
    05/2013;
  • Source
    Article: Search for cold gas in z>2 damped Lyman-alpha systems: 21-cm and H_2 absorption
    R. Srianand, N. Gupta, P. Petitjean, P. Noterdaeme, C. Ledoux, C. J. Salter, D. J. Saikia
    [show abstract] [hide abstract]
    ABSTRACT: (Abridged) We present the results of a systematic GBT and GMRT survey for 21-cm absorption in a sample of 10 DLAs at 2<z_abs<3.4. Analysis of L-band VLBA images of the background QSOs are also presented. We detect 21-cm absorption in only one DLA (at z_abs = 3.1745 towards J1337+3152). Combining our data with the data from the literature (a sample of 28 DLAs) and assuming the measured core fraction at milliarcsecond scale to represent the gas covering factor, we find that the HI gas in DLAs at z> 2 is predominantly constituted by WNM. The detection rate of 21-cm absorption seems to be higher for systems with higher N(HI) or metallicity. However, no clear correlation is found between the integrated 21-cm optical depth (or spin temperature) and either N(HI), metallicity or velocity spread of the low ionization species. There are 13 DLAs in our sample for which high resolution optical spectra covering the expected wavelength range of H_2 absorption are available. We report the detection of H_2 molecules in the z_abs = 3.3871 21-cm absorber towards J0203+1134 (PKS 0201+113). In 8 cases, neither H_2 nor 21-cm absorption are detected. The lack of 21-cm and H_2 absorption in these systems can be explained if most of the HI in these DLAs originate from low density high temperature gas. In one case we have a DLA with 21-cm absorption not showing H_2 absorption. In two cases, both species are detected but do not originate from the same velocity component. In the remaining 2 cases 21-cm absorption is not detected despite the presence of H_2 with evidence for the presence of cold gas. All this is consistent with the idea that the H_2 components seen in DLAs are compact (with sizes of < 15 pc) and contain only a small fraction (i.e typically <10%) of the total N(HI) measured in the DLAs.
    12/2011;
  • Source
    Article: Radio Polarimetry of 3C119, 3C318, and 3C343 at milliarcsecond resolution
    F. Mantovani, A. Rossetti, W. Junor, D. J. Saikia, C. J. Salter
    [show abstract] [hide abstract]
    ABSTRACT: We report VLBA polarimetric observations of the CSS sources 3C119, 3C318, and 3C343 at 5 and 8.4 GHz. The CSS source 3C119 has source rest-frame RM values up to ~10200 rad/m**2 in a region which coincides with a change in the direction of the inner jet. This component is located ~325 pc from the core, which is variable and has a peaked radio spectrum. In the case of 3C318, a rest-frame RM of ~3030 rad/m**2 has been estimated for the brightest component which contributes almost all of the polarised emission. Further, two more extended components have been detected, clearly showing "wiggles" in the jet towards the southern side of the source. The CSS source 3C343 contains two peaks of emission and a curved jet embedded in more diffuse emission. It exhibits complex field directions near the emission peaks, which indicate rest-frame RM values in excess of ~6000 rad/m**2. The locations of the cores in 3C318 and 3C343 are not clear. The available data on mas-scale rest-frame RM estimates for CSS sources show that these have a wide range of values extending up to ~40000 rad/m**2 in the central region of OQ172, and could be located at projected distances from the core of up to ~1600 pc, as in 3C43 where this feature has a rest-frame RM of ~14000 rad/m**2. RM estimates for cores in core-dominated radio sources indicate that in addition to responding to an overall density gradient of the magneto-ionic medium, geometry, orientation and modes of fuelling may also play a significant role. In addition to these effects, the high values of RM in CSS sources are possibly due to dense clouds of gas interacting with the radio jets. The observed distortions in the radio structures of many CSS sources are consistent with this interpretation. Comment: 15 pages, 190 figures. Accepted for publication in A&A
    05/2010;
  • Source
    Article: The Discovery of Host Galaxy HI Absorption in CTA 21
    C. J. Salter, D. J. Saikia, R. Minchin, T. Ghosh, Y. Chandola
    [show abstract] [hide abstract]
    ABSTRACT: We report the discovery of HI 21-cm absorption towards the well-studied GHz Peaked-Spectrum source CTA 21 (4C 16.09) using the Arecibo Telescope on 2009 September 20 and 21. Recently, the frequency band between 700 and 800 MHz was temporarily opened up to radio astronomy when US TV stations were mandated to switch from analog to digital transmissions, with new frequency allocations. The redshifted HI frequency for CTA 21 falls within this band. CTA 21 has a complex radio structure on a range of scales. The innermost prominent components are separated by ~12 mas while weak diffuse emission extends for up to ~300 mas. The HI absorption profile that we find has two main components, one narrow, the other wider and blue-shifted. The total HI column density is 7.9 x 10^20 cm^-2, assuming a covering factor of unity and a spin temperature of 100 K. This HI absorption confirms the recently determined optical redshift of this faint galaxy of z ~ 0.907. We discuss this new detection in the light of HI absorption studies towards compact radio sources, and also the possibility that CTA 21 may be exhibiting multiple cycles of nuclear activity. This new detection in CTA 21 is consistent with a strong trend for detection of HI absorption in radio galaxies with evidence of episodic nuclear/jet activity. Comment: Accepted for publication in ApJL
    04/2010;
  • Source
    Article: VLBA polarimetric observations of the CSS quasar 3C147
    A. Rossetti, F. Mantovani, D. Dallacasa, W. Junor, C. J. Salter, D. J. Saikia
    [show abstract] [hide abstract]
    ABSTRACT: Aims. We report new VLBA polarimetric observations of the compact steep-spectrum (CSS) quasar 3C147 (B0538+498) at 5 and 8.4GHz. Methods. By using multifrequency VLBA observations, we derived milliarcsecond-resolution images of the total intensity, polarisation, and rotation measure distributions, by combining our new observations with archival data. Results. The source shows a one-sided structure, with a compact region, and a component extending about 200 mas to the south-west. The compact region is resolved into two main components with polarised emission, a complex rotation measure distribution, and a magnetic field dominated by components perpendicular to the source axis. Conclusions. By considering all the available data, we examine the possible location of the core component, and discuss two possible interpretations of the observed structure of this source: core-jet and lobe-hot spot. Further observations to unambiguously determine the location of the core would help distinguish between the two possibilities discussed here. Comment: 11 pages, 12 figures
    10/2009;
  • Article: Large differential Faraday rotation in the compact steep‐spectrum quasar 3C 147 and jet–medium interactions
    W. Junor, C. J. Salter, D. J. Saikia, F. Mantovani, A. B. Peck
    [show abstract] [hide abstract]
    ABSTRACT: We present multifrequency radio observations of the prototypical compact steep-spectrum quasar 3C 147, and report enormous differential Faraday rotation between the two extended components on opposite sides of the quasar. This indicates that large amounts of thermal gas are present, and demonstrates directly the existence of asymmetries in the gaseous environment of this source. We suggest a consistent picture for 3C 147, and comment on the evolution of compact steep-spectrum radio sources in general.
    Monthly Notices of the Royal Astronomical Society 10/2008; 308(4):955 - 960. · 4.90 Impact Factor
  • Source
    Article: The Arecibo Arp 220 Spectral Census I: Discovery of the Pre-Biotic Molecule Methanimine and New Cm-wavelength Transitions of Other Molecules
    C. J. Salter, T. Ghosh, B. Catinella, M. Lebron, M. S. Lerner, R. Minchin, E. Momjian
    [show abstract] [hide abstract]
    ABSTRACT: An on-going Arecibo line search between 1.1 and 10 GHz of the prototypical starburst/megamaser galaxy, Arp 220, has revealed a spectrum rich in molecular transitions. These include the ``pre-biotic'' molecules: methanimine (CH$_{2}$NH) in emission, three $v_{2}=1$ direct l-type absorption lines of HCN, and an absorption feature likely to be from either $^{18}$OH or formic acid (HCOOH). In addition, we report the detection of two, possibly three, transitions of $\lambda$4-cm excited OH not previously detected in Arp~220 which are seen in absorption, and a possible absorption feature from the 6.668-GHz line of methanol. This marks the first distant extragalactic detection of methanimine, a pre-biotic molecule. Also, if confirmed, the possible methanol absorption line presented here would represent the first extragalactic detection of methanol at a distance further than 10 Mpc. In addition, the strong, previously undetected, cm-wave HCN $v_{2}=1$ direct l-type lines will aid the study of dense molecular gas and active star-forming regions in this starburst galaxy. Comment: 25 pages, 10 figures. Accepted for publication in AJ
    05/2008;
  • Source
    Article: Probing radio source environments via HI and OH absorption
    Neeraj Gupta, C. J. Salter, D. J. Saikia, T. Ghosh, S. Jeyakumar
    [show abstract] [hide abstract]
    ABSTRACT: We present the results of HI and OH absorption measurements towards a sample of radio sources using the Arecibo 305-m telescope and the GMRT. In total, 27 radio sources were searched for associated 21-cm HI absorption. One totally new HI absorption system was detected against the radio galaxy 3C258, while five previously known HI absorption systems, and one galaxy detected in emission, were studied with improved frequency resolution and/or sensitivity. Our sample included 17 GPS and CSS objects, 4 of which exhibit HI absorption. This detection rate of ~25% compares with a value of ~40% by Vermeulen et al. for similar sources. We detected neither OH emission nor absorption towards any of the sources that were observed at Arecibo, and estimate a limit on the abundance ratio of N(HI)/N(OH)>4x10^6 for 3C258. We have combined our results with those from other available HI searches to compile a heterogeneous sample of 96 radio sources consisting of 27 GPS, 35 CSS, 13 flat spectrum and 21 large sources. The HI absorption detection rate is highest (~45%) for the GPS sources and least for the large sources. We find HI column density to be anticorrelated with source size, as reported earlier by Pihlstr\"om et al. The HI column density shows no significant dependence on either redshift or luminosity, which are themselves strongly correlated. These results suggest that the environments of radio sources on GPS/CSS scales are similar at different redshifts. Further, in accordance with the unification scheme, the GPS/CSS galaxies have an HI detection rate of ~40% which is significantly higher than the detection rate (~20%) towards the GPS/CSS quasars. Also, the principal (strongest) absorption component detected towards GPS sources appears blue-shifted in ~65% of the cases, in agreement with the growing evidence for jet-cloud interactions. Comment: Abridged abstract, 22 pages, 21 figures, moderately revised, accepted for publication in MNRAS
    05/2006;
  • Source
    Article: VLBA Polarimetric Observations of Young Radio Sources
    F. Mantovani, A. Rossetti, W. Junor, D. J. Saikia, C. J. Salter
    [show abstract] [hide abstract]
    ABSTRACT: A VLBA polarimetric study of a sample of CSSs mainly associated with quasars has been made to investigate the polarization characteristics of their jets, lobes and cores, and possible jet-cloud interactions.
    11/2005; 340:186.
  • Source
    Article: Polarization Properties of Extragalactic Radio Sources
    D J Saikia, C J Salter
    11/2003; 26:93-144.
  • Source
    Article: Symmetry Parameters of CSS Sources: Evidence of Fuelling?
    D. J. Saikia, S. Jeyakumar, F. Mantovani, C. J. Salter, R. E. Spencer, P. Thomasson, P. J. Wiita
    [show abstract] [hide abstract]
    ABSTRACT: The compact steep spectrum (CSS) and gigahertz peaked spectrum (GPS) sources are widely believed to be young radiosources, with ages <10^6 yr. If the activity in the nucleus is fuelled by the supply of gas, one might find evidence of this gas by studying the structural and polarisation characteristics of CSS sources and their evolution through this gas. In this paper we discuss some of the possible `smoking-gun' evidence of this gas which may have triggered and fuelled the radio source. Comment: 11 pages, 8 figures
    05/2003;
  • Source
    Article: CSSs in a sample of B2 radio sources of intermediate strength
    D. J. Saikia, P. Thomasson, R. E. Spencer, F. Mantovani, C. J. Salter, S. Jeyakumar
    [show abstract] [hide abstract]
    ABSTRACT: We present radio observations of 19 candidate compact steep-spectrum (CSS) objects selected from a well-defined, complete sample of 52 B2 radio sources of intermediate strength. These observations were made with the VLA A-array at 4.835 GHz. The radio structures of the entire sample are summarised and the brightness asymmetries within the compact sources are compared with those of the more extended ones, as well as with those in the 3CRR sample and the CSSs from the B3-VLA sample. About 25 per cent of the CSS sources exhibit large brightness asymmetries, with a flux density ratio for the opposing lobes of $>$5, possibly due to interaction of the jets with infalling material. The corresponding percentage for the larger-sized objects is only about 5 per cent. We also investigate possible dependence of the flux density asymmetry of the lobes on redshift, since this might be affected by more interactions and mergers in the past. No such dependence is found. A few individual objects of interest are discussed in the paper. Comment: 10 pages, 7 figures, 2 tables; accepted for publication in Astronomy and Astrophysics
    06/2002;
  • Source
    Article: B1524-136: A CSS quasar with two-sided radio jets
    F. Mantovani, D. J. Saikia, M. Bondi, W. Junor, C. J. Salter, R. Ricci
    [show abstract] [hide abstract]
    ABSTRACT: We present MERLIN, global VLBI and VLBA observations of the high-luminosity, compact steep-spectrum quasar B1524$-$136 at cm wavelengths. These observations reveal well-defined radio jets on both sides of the active nucleus, a situation which is almost unique amongst high-luminosity radio quasars. However, the radio jets on opposite sides are very dissimilar, and the overall radio structure appears highly distorted. We discuss possible implications of these observations. Comment: 5 pages, 3 figures, to appear in A&A Letters
    05/2002;
  • Article: Polarization observations of the radio cores of AGN — I. A sample of quasars
    D. J. Saikia, G. F. Holmes, A. R. Kulkarni, C. J. Salter, S. T. Garrington
    [show abstract] [hide abstract]
    ABSTRACT: We present total-intensity and linear-polarization observations at a single epoch for a sample of 11 quasars and one BL Lac object. The data were taken with the VLA A array at λλ 20, 18, 6 and 2 cm. We examine the variation of the degree of polarization, p, and polarization position angle, PA, with wavelength, and attempt to determine the rotation measure, RM, of the cores in these sources. The degree of polarization does not exhibit any systematic variation with wavelength, the median values ranging from 2.3 to 3.5 per cent at the different wavelengths. The variation of PA with λ2 is not linear over the entire wavelength range. However, for most sources the λλ 20-, 18- and 6-cm PAs do follow such a linear relationship, yielding a median |RM| of about 15 rad m−2. In contrast, the λλ 6- and 2-cm observations give a median |RM| of about 129 rad m−2. The long-wavelength emission is likely to originate from a spatially different part of the milliarcsec-scale jet from the λ 2-cm emission, which could turn over at a higher frequency and is likely to be more compact and located closer to the quasar nucleus. We have attempted to obtain linear fits over the entire wavelength range allowing for n π ambiguities in the PAs, but the fits are not statistically significant. The low values of RM for these core-dominated sources suggest that either the radio emission from the jet intercepts few of the emission-line clouds and their confining medium, or the clouds have a small filling factor and are possibly magnetically confined.
    Monthly Notices of the Royal Astronomical Society 04/2002; 298(3):877 - 887. · 4.90 Impact Factor
  • Source
    Article: Compact steep-spectrum sources from the S4 sample
    D. J. Saikia, S. Jeyakumar, C. J. Salter, P. Thomasson, R. E. Spencer, F. Mantovani
    [show abstract] [hide abstract]
    ABSTRACT: We present the results of 5-GHz observations with the VLA A-array of a sample of candidate Compact Steep Spectrum sources (CSSs) selected from the S4 survey. We also estimate the symmetry parameters of high-luminosity CSSs selected from different samples of radio sources, and compare these with the larger sources of similar luminosity to understand their evolution and the consistency of the CSSs with the unified scheme for radio galaxies and quasars. The majority of CSSs are likely to be young sources advancing outwards through a dense asymmetric environment. The radio properties of CSSs are found to be consistent with the unified scheme, in which the axes of the quasars are observed close to the line of sight, while radio galaxies are observed close to the plane of the sky. Comment: accepted for publication in mnras; 8 pages, figure 1 with 21 images, and two additional figures; 2 tables
    09/2000;
  • Source
    Article: Some home-truths about small samples and counting statistics
    C. J. Salter, Dilip G. Banhatti
    [show abstract] [hide abstract]
    ABSTRACT: Assessing a fluctuation in the sky density of astronomical objects uses counting (i.e., Poisson) statistics for estimating errors. For a finite sample, there is a limit to the maximum possible fluctuation from the mean in units of the rms. This maximum is derived, and an example is used to illustrate these concepts.
    Bulletin of the Astronomical Society of India 01/2000; 28:363-365. · 2.72 Impact Factor
  • Source
    Article: An intrinsically asymmetric radio galaxy: 0500+630?
    D. J. Saikia, P. Thomasson, N. Jackson, C. J. Salter, W. Junor
    [show abstract] [hide abstract]
    ABSTRACT: As part of a search for high-luminosity radio galaxies with one-sided structures, the radio galaxy 0500+630 has been imaged with both the VLA and MERLIN and its optical spectrum determined using the Isaac Newton Telescope on La Palma. The galaxy is found to have a redshift of 0.290+/-0.004. The radio observations show the source to be highly asymmetric, with an overall structure which cannot be understood easily by ascribing it either to orientation and relativistic beaming effects or to an asymmetric distribution of gas in the central region. A comparison of this source with objects of similar luminosity suggests that it is one of the best examples yet of a source with possibly an intrinsic asymmetry in either the collimation of its jets or the supply of energy from the central engine to opposite sides.
    Monthly Notices of the Royal Astronomical Society 09/1996; 282:837-844. · 4.90 Impact Factor
  • Source
    Article: Millimeter-wavelength observations of compact steep-spectrum sources.
    H. Steppe, S. Jeyakumar, D. J. Saikia, C. J. Salter
    [show abstract] [hide abstract]
    ABSTRACT: Using the IRAM 30-m telescope, we have measured 90- and 230-GHz flux densities for a sample of 76 sources, about 70 of which are compact steep-spectrum radio sources (CSSs). These flux densities have been used to extend the radio spectra of the CSSs to millimeter wavelengths, and look for deviations of their high-frequency spectra from the trends established at lower frequencies. Since flat-spectrum, cm-wavelength, nuclear components have been detected in some of these sources, it is possible that such radio cores are self-absorbed at cm wavelengths, but could make their presence felt in the mm range via a flattening of the integrated spectrum. Alternatively, if the nucleus is no longer active and there is no fresh supply of energy to the extended features, one might find high-frequency spectral steepening caused by radiative losses. In this paper we present the results of our observations and discuss their implications.
    Astronomy and Astrophysics Supplement Series 10/1995; 113:409.
  • Source
    Article: Total power and polarization measurements of the supernova remnant CTB104A at 4.75 GHz
    F. Mantovani, P. Tomasi, C. J. Salter
    [show abstract] [hide abstract]
    ABSTRACT: Observations of both total-intensity and linearly-polarized emission from CTB104A and its protrusions to investigate the spectral-index distribution and polarization characteristics of the remnant. The nonthermal spectra of the protrusions suggest that they are associated with the main body, and the strong depolarization at lower frequencies is confirmed. Three of the protrusions exhibit notable polarization, and the possible association of the supernova remnant and a nearby CO cloud is postulated.
    Astronomy and Astrophysics 06/1991; 247:545-550. · 4.59 Impact Factor
  • Source
    Article: The Ooty Summer Training Program 1990
    D. J. Saikia, C. J. Salter, D. G. Banhatti, T. Ghosh, P. Gothoskar, P. K. Manoharan
    Bulletin of the Astronomical Society of India 02/1991; 19:109. · 2.72 Impact Factor
1 2 Next »

Institutions

  • 2002–2008
    • University of Puerto Rico at Arecibo
      Arecibo, Arecibo, Puerto Rico
  • 1985–1991
    • Tata Institute of Fundamental Research
      Mumbai, State of Maharashtra, India
  • 1982
    • National Centre For Radio Astrophysics - Tata Institute Of Fundamental Research
      Pune, State of Maharashtra, India
  • 1981
    • Max-Planck-Institut für Radioastronomie
      Bonn, North Rhine-Westphalia, Germany
Browse more researchers