New Detections of Galactic Molecular Absorption Systems toward ALMA Calibrator Sources

We report on Atacama Large Millimeter/submillimeter Array (ALMA) detections of molecular absorption lines in Bands 3, 6 and 7 toward four radio-loud quasars, which were observed as the bandpass and complex gain calibrators. The absorption systems, three of which are newly detected, are found to be Galactic origin. Moreover, HCO absorption lines toward two objects are detected, which almost doubles the number of HCO absorption samples in the Galactic diffuse medium. In addition, high HCO to H13CO+ column density ratios are found, suggesting that the interstellar media (ISM) observed toward the two calibrators are in photodissociation regions, which observationally illustrates the chemistry of diffuse ISM driven by ultraviolet (UV) radiation. These results demonstrate that calibrators in the ALMA Archive are potential sources for the quest for new absorption systems and for detailed investigation of the nature of the ISM.

[1]  K. Menten,et al.  [C II] absorption and emission in the diffuse interstellar medium across the Galactic plane , 2014, 1410.4663.

[2]  Santiago,et al.  An ALMA Early Science survey of molecular absorption lines toward PKS 1830−211 - Analysis of the absorption profiles , 2014, 1404.7667.

[3]  M. Gerin,et al.  HCO, c-C3H and CF+: three new molecules in diffuse, translucent and “spiral-arm” clouds , 2014, 1403.3531.

[4]  P. Goldsmith,et al.  A Herschel [C ii] Galactic plane survey - I. The global distribution of ISM gas components , 2013, 1304.7770.

[5]  S. Iguchi,et al.  A MILLIMETER-WAVE INTERFEROMETRIC SEARCH FOR A MOLECULAR TORUS IN THE RADIO GALAXY NGC 4261 , 2013 .

[6]  C. Kramer,et al.  THE PLATEAU DE BURE + 30 m ARCSECOND WHIRLPOOL SURVEY REVEALS A THICK DISK OF DIFFUSE MOLECULAR GAS IN THE M51 GALAXY , 2013, 1304.1396.

[7]  T. Sawada,et al.  STRUCTURAL VARIATION OF MOLECULAR GAS IN THE SAGITTARIUS ARM AND INTERARM REGIONS , 2012, 1204.5687.

[8]  James G. Ingalls,et al.  SPITZER INFRARED SPECTROGRAPH DETECTION OF MOLECULAR HYDROGEN ROTATIONAL EMISSION TOWARDS TRANSLUCENT CLOUDS , 2011, 1109.2544.

[9]  A. Kemball,et al.  THE SEARCH FOR EXTRAGALACTIC LITHIUM HYDRIDE , 2011, 1106.2471.

[10]  T. Wiklind,et al.  On the absence of molecular absorption in high-redshift millimetre-band searches , 2011, 1106.0578.

[11]  Germany,et al.  Molecules at z = 0.89 - A 4-mm-rest-frame absorption-line survey toward PKS 1830−211 , 2011, 1104.3361.

[12]  B. Draine.  Physics of the Interstellar and Intergalactic Medium , 2011 .

[13]  D. Iono,et al.  DISENTANGLING THE CIRCUMNUCLEAR ENVIRONS OF CENTAURUS A. II. ON THE NATURE OF THE BROAD ABSORPTION LINE , 2010, 1007.2061.

[14]  M. Gerin,et al.  Molecular absorption lines toward star-forming regions: a comparative study of HCO+, HNC, HCN, and CN , 2010, 1006.0582.

[15]  S. Viti,et al.  PHOTODISSOCIATION CHEMISTRY FOOTPRINTS IN THE STARBURST GALAXY NGC 253 , 2009, 0911.2673.

[16]  J. Ott,et al.  The density, the cosmic microwave background, and the proton-to-electron mass ratio in a cloud at redshift 0.9 , 2009, 0904.3081.

[17]  J. Goicoechea,et al.  HCO mapping of the Horsehead: tracing the illuminated dense molecular cloud surfaces , 2008, 0811.1470.

[18]  F. Combes.  Molecular absorptions in high-z objects , 2007, astro-ph/0701894.

[19]  Holger S. P. Müller,et al.  The Cologne Database for Molecular Spectroscopy, CDMS: a useful tool for astronomers and spectroscopists , 2005 .

[20]  Yasuo Fukui,et al.  A Complete Search for Dense Cloud Cores in Taurus , 2002 .

[21]  R. Neri,et al.  Widespread HCO Emission in the Nuclear Starburst of M82 , 2002, astro-ph/0207313.

[22]  W. Reach,et al.  Photoelectric Heating and [C II] Cooling of High Galactic Latitude Translucent Clouds , 2002, astro-ph/0207264.

[23]  P. Schilke,et al.  Observations of SiO towards photon dominated regions , 2001 .

[24]  Alexander G. G. M. Tielens,et al.  Photodissociation Regions in the Interstellar Medium of Galaxies , 1999 .

[25]  Holger S. P. Müller,et al.  THE COLOGNE DATABASE FOR MOLECULAR SPECTROSCOPY, CDMS , 2001 .

[26]  J. M. Hollis,et al.  HCO emission from H II-molecular cloud interface regions. , 1988, The Astrophysical journal.

[27]  H. Müller,et al.  Submillimeter, millimeter, and microwave spectral line catalog. , 1985, Applied optics.

[28]  S. Kulkarni,et al.  A survey of HI absorption at low latitudes , 1983 .

[29]  M. S. Roberts.  THE DETECTION OF 21-CENTIMETER HYDROGEN ABSORPTION ARISING FROM WITHIN THE RADIO GALAXY CENTAURUS A. , 1970 .