Resolving the Radio Emission from the Quasar P172+18 at $z = 6.82$

We present high angular resolution imaging of the quasar PSO J172.3556+18.7734 at $z=6.82$ with the Very Long Baseline Array (VLBA). This source currently holds the record of being the highest redshift radio-loud quasar. These observations reveal a dominant radio source with a flux density of $398.4 pm 61.4~mu$Jy at 1.53 GHz, a deconvolved size of $9.9 times 3.5$ mas ($52.5 times 18.6$ pc), and an intrinsic brightness temperature of ($4.7 pm 0.7) times 10^7$ K. A weak unresolved radio extension from the main source is also detected at $sim~3.1sigma$ level. The total flux density recovered with the VLBA at 1.53 GHz is consistent with that measured with the Very Large Array (VLA) at a similar frequency. The quasar is not detected at 4.67 GHz with the VLBA, suggesting a steep spectral index with a limit of $alpha^{1.53}_{4.67} < -$1.55. The quasar is also not detected with the VLBA at 7.67 GHz. The overall characteristics of the quasar suggest that it is a very young radio source similar to lower redshift Gigahertz Peaked Spectrum radio sources, with an estimated kinematic age of $sim~10^3$ years. The VLA observations of this quasar revealed a second radio source in the field $23rlap{.}{}1$ away. This radio source, which does not have an optical or IR counterpart, is not detected with the VLBA at any of the observed frequencies. Its non-detection at the lowest observed VLBA frequency suggests that it is resolved out, implying a size larger than ~$0rlap{.}{}17$. It is thus likely situated at lower redshift than the quasar.

The Zeeman Effect in the 44 GHz Class I Methanol (CH3OH) Maser Line Toward DR21W

We report the detection of the Zeeman effect in the 44 GHz Class I methanol maser line toward the high mass star forming region DR21W. There are two prominent maser spots in DR21W at the ends of a northwest-southeast linear arrangement. For the maser at the northwestern end (maser A), we fit three Gaussian components. In the strongest component, we obtain a significant Zeeman detection, with $zB_{rm los}=-23.4pm3.2$ Hz. If we use $z=-0.920$ Hz mG$^{-1}$ for the $F=5 rightarrow 4$ hyperfine transition, this corresponds to a magnetic field $|B_{rm los}|=25.4$ mG; $B_{rm los}$ would be higher if a different hyperfine was responsible for the 44 GHz maser, but our results also rule out some hyperfines, since fields in these regions cannot be hundreds of mG. Class I methanol masers form in outflows where shocks compress magnetic fields in proportion to gas density. Designating our detected $B_{rm los}=25$ mG as the magnetic field in the post-shock gas, we find that $B_{rm los}$ in the pre-shock gas should be 0.1-0.8 mG. Although there are no thermal-line Zeeman detections toward DR21W, such values are in good agreement with Zeeman measurements in the CN thermal line of 0.36 and 0.71 mG about $3.5$ away in DR21(OH) in gas of comparable density to the pre-shock gas density in DR21W. Comparison of our derived magnetic energy density to the kinetic energy density in DR21W indicates that magnetic fields likely play a significant role in shaping the dynamics of the post-shocked gas in DR21W.

Resolving the Powerful Radio-loud Quasar at z~6

We present high angular resolution imaging ($23.9 times 11.3$ mas, $138.6 times 65.5$ pc) of the radio-loud quasar PSO~J352.4034$-$15.3373 at $z=5.84$ with the Very Long Baseline Array (VLBA) at 1.54 GHz. This quasar has the highest radio-to-optical flux density ratio at such a redshift, making it the radio-loudest source known to date at $z sim 6$. The VLBA observations presented here resolve this quasar into multiple components with an overall linear extent of 1.62 kpc ($0rlap{.}{}28$) and with a total flux density of $6.57 pm 0.38$ mJy, which is about half of the emission measured at a much lower angular resolution. The morphology of the source is comparable with either a radio core with a one-sided jet, or a compact or a medium-size Symmetric Object (CSO/MSO). If the source is a CSO/MSO, and assuming an advance speed of $0.2c$, then the estimated kinematic age is $sim 10^4$ yr.

The Zeeman Effect in the 44 GHz Class I Methanol Maser Line toward DR21(OH)

We report the detection of the Zeeman effect in the 44 GHz Class I methanol maser line toward the star forming region DR21(OH). In a 219 Jy/beam maser centered at an LSR velocity of 0.83 km s$^{-1}$, we find a 20-$sigma$ detection of $zB_{text{los}} = 53.5 pm 2.7$ Hz. If 44 GHz methanol masers are excited at $n sim 10^{7-8}$ cm$^{-3}$, then the $B~vs.~n^{1/2}$ relation would imply from comparison with Zeeman effect detections in the CN($1-0$) line toward DR21(OH) that magnetic fields traced by 44 GHz methanol masers in DR21(OH) should be $sim$10 mG. Together with our detected $zB_{text{los}} = 53.5$ Hz, this would imply that the value of the 44 GHz methanol Zeeman splitting factor $z$ is $sim$5 Hz mG$^{-1}$. Such small values of $z$ would not be a surprise, as the methanol molecule is non paramagnetic, like H$_2$O. Empirical attempts to determine $z$, as demonstrated, are important because currently there are no laboratory measurements or theoretically calculated values of $z$ for the 44 GHz methanol transition. Data from observations of a larger number of sources are needed to make such empirical determinations robust.

The Highest Redshift Quasar at $z=7.085$: A Radio Quiet Source

We present 1-2 GHz Very Large Array A-configuration continuum observations on the highest redshift quasar known to date, the $z=7.085$ quasar ULAS J112001.48+064124.3. The results show no radio continuum emission at the optical position of the quasar or its vicinity at a level of $geq 3sigma$ or $23.1 mu$Jy beam$^{-1}$. This $3sigma$ limit corresponds to a rest frame 1.4 GHz luminosity density limit of $L_{ u,1.4,GHz} < 1.76 times 10^{24}$ W Hz$^{-1}$ for a spectral index of $alpha=0$, and $L_{ u,1.4,GHz} < 1.42 times 10^{25}$ W Hz$^{-1}$ for a spectral index of $alpha=-1$. The rest-frame 1.4 GHz luminosity limits are $L_{rad} < 6.43 times 10^6 L_{odot}$ and $L_{rm rad} < 5.20 times 10^7 L_{odot}$ for $alpha=0$ and $alpha=-1$, respectively. The derived limits for the ratio of the rest frame 1.4 GHz luminosity density to the $B$-band optical luminosity density are $Rrlap{}_{1.4}^{*} < 0.53$ and $< 4.30$ for the above noted spectral indices, respectively. Given our upper limits on the radio continuum emission and the radio-to-optical luminosity ratio, we conclude that this quasar is radio-quiet and located at the low end of the radio quiet distribution of high redshift ($z gtrsim 6$) quasars.

Comparison of Two Epochs of the Zeeman Effect in the 44 GHz Class I methanol (CH3OH) maser line in OMC-2

We present a second epoch of observations of the 44 GHz Class I methanol maser line toward the star forming region OMC-2. The observations were carried out with the Very Large Array, and constitute one of the first successful Zeeman effect detections with the new WIDAR correlator. Comparing to the result of our earlier epoch of data for this region, we find that the intensity of the maser increased by 50%, but the magnetic field value has stayed the same, within the errors. This suggests that the methanol maser may be tracing the large-scale magnetic field that is not affected by the bulk gas motions or turbulence on smaller scales that is causing the change in maser intensity.

Very Large Array Detection of the 36 GHz Zeeman Effect in DR21W Revisited

We report on the observation of the 36 GHz methanol maser line in the star forming region DR21W to accurately measure the Zeeman effect. The reported Zeeman signature by Fish et al. (2011) became suspicious after an instrumental effect was discovered in the early days of the Very Large Array Wide-band Digital Architecture (WIDAR) correlator commissioning. We conclude that the previously reported magnetic field strength of 58 mG ((1.7 Hz/mG)/z) is instrumental in nature and thus incorrect. With the improved performance of the array, we now deduce a 3 sigma limit of -4.7 to +0.4 mG ((1.7 Hz/mG)/z) for the line-of-sight component of the magnetic field strength in DR21W.

High Sensitivity Array Observations of the z=1.87 Sub-Millimeter Galaxy GOODS 850-3

We present sensitive phase-referenced VLBI results on the radio continuum emission from the z=1.87 luminous submillimeter galaxy (SMG) GOODS 850-3. The observations were carried out at 1.4 GHz using the High Sensitivity Array (HSA). Our sensitive tapered VLBI image of GOODS 850-3 at 0.47 x 0.34 arcsec (3.9 x 2.9 kpc) resolution shows a marginally resolved continuum structure with a peak flux density of 148 pm 38 uJy/beam, and a total flux density of 168 pm 73 uJy, consistent with previous VLA and MERLIN measurements. The derived intrinsic brightness temperature is > 5 pm 2 x 10^3 K. The radio continuum position of this galaxy coincides with a bright and extended near-infrared source that nearly disappears in the deep HST optical image, indicating a dusty source of nearly 9 kpc in diameter. No continuum emission is detected at the full VLBI resolution (13.2 x 7.2 mas, 111 x 61 pc), with a 4-sigma point source upper limit of 26 uJy/beam, or an upper limit to the intrinsic brightness temperature of 4.7 x 10^5 K. The extent of the observed continuum source at 1.4 GHz and the derived brightness temperature limits are consistent with the radio emission (and thus presumably the far-infrared emission) being powered by a major starburst in GOODS 850-3, with a star formation rate of ~2500 M_sun/yr. Moreover, the absence of any continuum emission at the full resolution of the VLBI observations indicates the lack of a compact radio AGN source in this z=1.87 SMG.

VLA and VLBA Observations of the Highest Redshift Radio-Loud QSO J1427+3312 at z = 6.12

We present 8.4 GHz VLA A-array and 1.4 GHz VLBA results on the radio continuum emission from the highest redshift radio-loud quasar known to date, the $z=6.12$ QSO J1427+3312. The VLA observations show an unresolved steep spectrum source with a flux density of $250 pm 20$ uJy at 8.4GHz and a spectral index value of $alpha^{8.4}_{1.4}=-1.1$. The 1.4 GHz VLBA images reveal several continuum components with a total flux density of $1.778 pm 0.109$ mJy, which is consistent with the flux density measured with the VLA at 1.4 GHz. Each of these components is resolved with sizes of a few milliarcseconds, and intrinsic brightness temperatures on the order of $10^7$ to $10^8$ K. The physical characteristics as revealed in these observations suggest that this QSO may be a Compact Symmetric Object, with the two dominant components seen with the VLBA, which are separated by 31 mas (174 pc) and have intrinsic sizes of ~22-34 pc, being the two radio lobes that are confined by the dense ISM. If indeed a CSO, then the estimated kinematic age of this radio AGN is only $10^3$ yr.

The Arecibo Arp 220 Spectral Census I: Discovery of the Pre-Biotic Molecule Methanimine and New Cm-wavelength Transitions of Other Molecules

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.