arXiv subjects

A. B. Peck

Publications and source records attributed to A. B. Peck.

At least 55 records · Page 3Linked to original sources

arXiv2003

Breaking All the Rules: The Compact Symmetric Object 0402+379

We present results of multi-frequency VLBA observations of the compact symmetric object (CSO) 0402+379. The parsec-scale morphology of 0402+379 allows us to confirm it as a CSO, while VLA data clearly show the presence of kiloparsec-scale structure. Thus, 0402+379 is only the second known CSO to possess large scale structure. Another puzzling morphological characteristic found from our observations is the presence of two central, compact, flat-spectrum components, which we identify as possible active nuclei. We also present the discovery of neutral hydrogen absorption along the southern hotspot of 0402+379 with a central velocity ~1000 km/s greater than the systemic velocity. Multi-epoch observations from the VLA archive, the Caltech-Jodrell Bank Survey, and the VLBA Calibrator Survey allow us to further analyze these anomalous features. Results of this analysis reveal significant motion in the northern hotspot, as well as appreciable variability in both of the core candidates. We consider the possibility that 0402+379 was formed during a recent merger. In this case, the two candidate cores could be interpreted as binary supermassive black holes that have not yet coalesced, whereas the large-scale radio emission could be attributed to interactions directly linked to the merger or to previous activity associated with one of the cores.

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arXiv2003

Water vapor in the starburst galaxy NGC 253: A new nuclear maser?

22 GHz water vapor emission was observed toward the central region of the spiral starburst galaxy NGC 253. Monitoring observations with the 100-m telescope at Effelsberg and measurements with the BnC array of the VLA reveal three distinct velocity components, all of them blueshifted with respect to the systemic velocity. The main component arises from a region close to the dynamical center and is displaced by <1 arcsec from the putative nuclear continuum source. The bulk of this maser component is spread over an area not larger than 70 x 50 mas. Its radial velocity may be explained by masing gas that is part of a nuclear accretion disk or of a counterrotating kinematical subsystem or by gas that is entrained by the nuclear superwind or by an expanding supernova shell. A weaker feature, located 5 arcsec to the northeast, is likely related to an optically obscured site of massive star formation.

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arXiv2003

Extragalactic water masers in bright IRAS sources

We report the results of a search for 22 GHz water maser emission in IRAS-bright galaxies, using the 100-m Effelsberg telescope. In particular, we present the details of four new maser detections (IC342, NGC2146, NGC3556, and Arp299) and follow-up interferometric studies. A comparison between water maser detection rates derived in the present study and those in previous similar surveys is also presented.

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arXiv2003

Neutral hydrogen absorption at the center of NGC2146

We present 1.4 GHz HI absorption line observations towards the starburst in NGC2146, made with the VLA and MERLIN. The HI absorption has a regular spatial and regular velocity distribution, and does not reveal any anomaly as a sign of an encounter with another galaxy or of a far-evolved merger.

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arXiv2003

Identifying Compact Symmetric Objects in the Southern Sky

We present results of multifrequency polarimetric VLBA observations of 20 compact radio sources. The observations represent the northern and southern extensions of a large survey undertaken to identify Compact Symmetric Objects (CSOs) Observed in the Northern Sky (COINS). CSOs are young radio galaxies whose jet axes lie close to the plane of the sky, and whose appearance is therefore not dominated by relativistic beaming effects. The small linear sizes of CSOs make them valuable for studies of both the evolution of radio galaxies and testing unified schemes for active galactic nuclei (AGN). In this paper we report on observations made of 20 new CSO candidates discovered in the northern and southern extremities of the VLBA Calibrator Survey. We identify 4 new CSOs, and discard 12 core-jet sources. The remaining 4 sources remain candidates pending further investigation. We present continuum images at 5 GHz and 15 GHz and, where relevant, images of the polarized flux density and spectral index distributions for the 8 new CSOs and CSO candidates.

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arXiv2003

The Flaring H2O Megamaser and Compact Radio Source in Mrk 348

We report on single-dish monitoring and extremely high angular resolution observations of the flaring H2O megamaser in the Seyfert 2 galaxy Mrk 348. The H2O line is redshifted by ~130 km/s with respect to the systemic velocity, is very broad, with a FWHM of 130 km/s, and has no detectable high velocity components within 1500 km/s on either side of the strong line. Monitoring observations made with the Effelsberg 100m telescope show that the maser varies significantly on timescales as short as one day and that the integrated line flux is loosely correlated with the continuum flux. VLBA observations indicate that the maser emission arises entirely from a region less than 0.25 pc in extent, located toward a continuum component thought to be associated with the receding jet. We also report on integrated flux monitoring with the VLA between 1.4 and 43 GHz, and VLBA continuum observations of the milliarcsecond scale jets at 1.7, 8, 15, and 22 GHz. These observations have allowed us to tentatively pinpoint the location of the core, and also show the ejection of a new jet component during the current radio "flare."

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arXiv2003

Dense gas in nearby galaxies: XV. Hot ammonia in NGC253, Maffei2 and IC342

The detection of NH3 inversion lines up to the (J,K)=(6,6) level is reported toward the central regions of the nearby galaxies NGC253, Maffei2, and IC342. The observed lines are up to 406K (for (J,K)=(6,6)) and 848K (for the (9,9) transition) above the ground state and reveal a warm (T_kin= 100 - 140 K) molecular component toward all galaxies studied. The tentatively detected (J,K)=(9,9) line is evidence for an even warmer (>400K) component toward IC342. Toward NGC253, IC342 and Maffei2 the global beam averaged NH3 abundances are 1-2 10^-8, while the abundance relative to warm H2 is around 10^-7. The temperatures and NH3 abundances are similar to values found for the Galactic central region. C-shocks produced in cloud-cloud collisions can explain kinetic temperatures and chemical abundances. In the central region of M82, however, the NH3 emitting gas component is comparatively cool (~ 30K). It must be dense (to provide sufficient NH3 excitation) and well shielded from dissociating photons and comprises only a small fraction of the molecular gas mass in M82. An important molecular component, which is warm and tenuous and characterized by a low ammonia abundance, can be seen mainly in CO. Photon dominated regions (PDRs) can explain both the high fraction of warm H_2 in M82 and the observed chemical abundances.

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arXiv2002

Observations of extragalactic masers in bright IRAS sources

We report the first results of an ongoing survey at 22 GHz with the 100-m Effelsberg telescope to search for water maser emission in bright IRAS sources. We have detected water vapor emission in IC 342. The maser, associated with a star forming region ~10-15 arcsec west of the nucleus, consists of a single 0.5 km/s wide feature and reaches an isotropic luminosity of 0.01 L(sun) (D = 1.8 Mpc). Our detection raises the detection rate among northern galaxies with IRAS point source fluxes S(100micron) > 50 Jy to 16%.

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arXiv2002

The association between water kilomasers and compact radio sources in the starburst galaxy NGC2146

We report the detection of 22 GHz water vapor emission toward the starburst galaxy NGC2146, made using the Effelsberg 100-m telescope. Interferometric observations with the Very Large Array (VLA) show that a part of the emission originates from two prominent sites of star formation that are associated with compact radio continuum sources, likely ultra-compact HII regions. It is concluded that the emission arises from the most luminous and distant water `kilomasers' detected so far. Our data increase the number of water maser detections in northern galaxies (Dec > -30 deg) with 100 micron IRAS point source fluxes > 50 Jy to 18%.

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arXiv2002

HI Absorption in the Gigamaser Galaxy TXS 2226-184 and the Relation between HI Absorption and Water Emission

We report on the discovery of HI in absorption toward the gigamaser galaxy TXS2226-184 using the VLA. The absorption appears to consist of two components -- one with a width of 125 km/s, and one broader (420 km/s), both toward the compact radio source in the nucleus of the galaxy. Based on these large velocity widths we suggest that the HI absorption is produced in the central parsecs of the galaxy, on a similar scale to that which gives rise to the water maser emission. This brings to eight the number of galaxies known to exhibit both water masers and HI absorption. We explore the relationship between these two phenomena, and present a physically motivated (but unfruitful) search for water maser emission in five radio galaxies known to exhibit strong HI absorption.

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arXiv2002

Water maser emission in IC342

The detection of 22 GHz water vapor emission from IC342 is reported, raising the detection rate among northern galaxies with 100 micron IRAS point source fluxes > 50 Jy to 16%. The maser, associated with a star forming region 10-15 arcsec west of the nucleus, consists of a single 0.5 km/s wide feature and reaches an isotropic luminosity of 0.01 solar luminosity (D = 1.8 Mpc). If the time variability is intrinsic, the maser size is < 1.5 x 10^(16) cm (< 0.5 mas) which corresponds to a brightness temperature of > 10^(9) K. The linewidth, luminosity, and rapid variability are reminiscent of the 8 km/s super maser in Orion-KL. A velocity shift of 1 km/s within two weeks and subsequent rapid fading is explained in terms of a chance alignment of two dense molecular clouds. Observations at 22 GHz toward Maffei2 are also reported, yielding a 5 sigma upper limit of 25 mJy for a channel spacing of 1.05 km/s.

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arXiv2002

The VLBA Calibrator Survey - VCS1

A catalog containing milliarcsecond--accurate positions of 1332 extragalactic radio sources distributed over the northern sky is presented - the Very Long Baseline Array Calibrator Survey (VCS1). The positions have been derived from astrometric analysis of dual-frequency 2.3 and 8.4 GHz VLBA snapshot observations; in a majority of cases, images of the sources are also available. These radio sources are suitable for use in geodetic and astrometric experiments, and as phase-reference calibrators in high-sensitivity astronomical imaging. The VCS1 is the largest high-resolution radio survey ever undertaken, and triples the number of sources available to the radio astronomy community for VLBI applications. In addition to the astrometric role, this survey can be used in active galactic nuclei, Galactic, gravitational lens and cosmological studies. The VCS1 catalog will soon be available at www.nrao.edu/vlba/VCS1 .

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arXiv2001

GRB 010222: A Burst Within a Starburst

We present millimeter and submillimeter wavelength observations and near-infrared K-band imaging toward the bright gamma-ray burst GRB 010222. Over seven epochs the flux density of the source was constant with an average flux density 3.74+/-0.53 mJy at 350 GHz and 1.05+/-0.22 mJy at 250 GHz, giving a spectral index alpha=3.78+/-0.25. We rule out the possibility that this emission originated from the burst or its afterglow and we conclude that it is due to a dusty, high redshift starburst galaxy (SMM J14522+4301). We argue that the host galaxy of GRB 010222 is the most plausible counterpart of SMM J14522+4301, based in part on the centimeter detection of the host at the expected level. The optical/NIR properties of the host galaxy of GRB 010222 suggest that it is a blue, sub-L_*, similar to other GRB host galaxies. This contrasts with the enormous far-infrared luminosity of this galaxy based on our submillimeter detection (L_Bol~4X10^{12} L_odot). We suggest that this GRB host galaxy has a very high star formation rate, SFR 600 M_\odot/yr, most of which is unseen at optical wavelengths.

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arXiv2001

VLBA Observations and Effelsberg Monitoring of a Flaring Water Maser in Mrk 348

We report on single-dish monitoring as well as extremely high angular resolution observations of the flaring H2O maser in the Seyfert 2 galaxy Mrk 348. The H2O line is redshifted by ~130 km/s with respect to the systemic velocity, is very broad, with a FWHM of 130 km/s, and has no detectable high velocity components within 1500 km/s on either side of the strong line. Monitoring observations made with the Effelsberg 100m telescope show that the maser varies significantly on timescales as short as one day. VLBA observations indicate that the maser emission arises entirely from a region less than 0.25 pc in extent, located toward a continuum component thought to be associated with the receding jet.

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arXiv2001

A Flaring Megamaser in Mrk 348

We report new observations of the H2O megamaser in the Seyfert 2 galaxy Mrk 348. Following our initial detection in 2000 March using the Effelsberg 100 m telescope, re-analysis of previous data on this source indicates that the maser was present but only marginally detectable in late 1997. Monitoring through late 2000 shows that the maser has again decreased to its original level. The H2O line is redshifted by ~130 km/s with respect to the systemic velocity, is extremely broad, with a FWHM of 130 km/s, and has no detectable high velocity components within 1500 km/s on either side of the strong line. Followup VLBA observations show that the maser emission emanates entirely from a region >0.25 pc in extent, toward the base of the radio jet.

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arXiv2001

Evidence for a Circumnuclear Disk in 1946+708

A number of extragalactic radio sources which exhibit symmetric jets on parsec scales have now been found to have neutral hydrogen absorption at or near the systemic velocities of their host galaxies. Understanding the spatial distribution and kinematics of the HI detected toward the central parsecs of these sources provides an important test of unified schemes for AGN. We present results of Global VLBI Network observations of the redshifted 21 cm HI line toward the Compact Symmetric Object 1946+708 (z=0.101). We find significant structure in the gas on parsec scales. The peak column density of the HI (N_HI~3x10^23 cm^-2(Ts/8000K)) occurs near the center of activity of the source, as does the highest velocity dispersion (FWHM 350 to 400 km/s). There is also good evidence for a torus of ionized gas with column density 7x10^22 cm^-2}. The jets in 1946+708 exhibit bi-directional motion measurable on timescales of a few years. The resulting unique information about the geometry of the continuum source greatly assists in the interpretation of the gas distribution, which is strongly suggestive of a circumnuclear torus of neutral atomic and ionized material with one or more additional compact clumps of gas along the line of sight to the approaching jet.

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arXiv2000

Dense Gas in Nearby Galaxies: XIV. Detection of hot ammonia in Maffei 2

The (J,K) = (1,1), (2,2), (3,3), and (4,4) inversion lines of ammonia (NH3) have been detected toward the nuclear 40'' sized bar of the nearby spiral galaxy Maffei 2. The relative intensities of the ammonia lines are characterized by a rotational temperature of 85 K. This is higher than rotational temperatures measured toward IC342 and most Galactic Center clouds, implying kinetic temperatures of at least 100 K. Since the kinetic temperature of the gas is larger than that of the dust, NH3 is tracing a particularly dense warm gas component that is heated by young massive stars, cloud-cloud collisions, or ion-slip heating in the nuclear starburst. The gas north of the nucleus (V(LSR} = -80 km/s) is more highly excited than the gas further south (+6 km/s). This asymmetry might be related to a pronounced morphological distortion that is observed in the north-eastern part of the galaxy.

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arXiv2000

Parsec-Scale Imaging of HI Absorption in 1946+708

In the last several years, a number of compact extragalactic radio sources have been found to exhibit neutral hydrogen absorption at or near the systemic velocities of their host galaxies. Models proposed to explain this phenomenon involve a circumnuclear torus of gas and dust. The orientation of this structure determines whether or not the central engine appears obscured. Understanding the spatial distribution and kinematics of the HI detected toward the central parsecs of these sources provides an important test of this model and of unified schemes for AGN. We present results of Global VLBI Network observations of the redshifted 21 cm HI line toward the Compact Symmetric Object 1946+708 (z=0.101). This source is of particular interest because it exhibits bi-directional motion measurable on timescales of a few years. The resulting unique information about the geometry of the continuum source greatly assists in the interpretation of the HI distribution. We find significant structure in the gas on parsec scales. The peak column density of the HI occurs near the center of activity of the source, as does the highest velocity dispersion (FWHM ~ 350 to 400 km/s). The distribution of gas in 1946+708 is strongly suggestive of a circumnuclear torus of atomic material with one or more additional compact clumps of gas along the line of sight to the approaching jet.

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