TY - JOUR

T1 - Signatures of UV radiation in low-mass protostars I. Origin of HCN and CN emission in the Serpens Main region

AU - Mirocha, Agnieszka

AU - Karska, Agata

AU - Gronowski, Marcin

AU - Kristensen, Lars E.

AU - Tychoniec, Lukasz

AU - Harsono, Daniel

AU - Figueira, Miguel

AU - Gladkowski, Marcin

AU - Zoltowski, Michal

PY - 2021/12/16

Y1 - 2021/12/16

N2 - Context. Ultraviolet radiation (UV) influences the physics and chemistry of star-forming regions, but its properties and significance in the immediate surroundings of low-mass protostars are still poorly understood.Aims. Our aim is to extend the use of the CN/HCN ratio, already established for high-mass protostars, to the low-mass regime to trace and characterize the UV field around low-mass protostars on similar to 0.6 x 0.6 pc scales.Methods. We present 5' x 5' maps of the Serpens Main Cloud encompassing ten protostars observed with the EMIR receiver at the IRAM 30 m telescope in CN 1-0, HCN 1-0, CS 3-2, and some of their isotopologs. The radiative-transfer code RADEX and the chemical model Nahoon were used to determine column densities of molecules, gas temperature and density, and the UV field strength, G(0).Results. The spatial distribution of HCN and CS are closely correlated with CO 6-5 emission, that traces outflows. The CN emission is extended from the central protostars to their immediate surroundings also tracing outflows, likely as a product of HCN photodissociation. The ratio of CN to HCN total column densities ranges from similar to 1 to 12 corresponding to G(0) approximate to 10(1) -10(3) for gas densities and temperatures typical for outflows of low-mass protostars.Conclusions. UV radiation associated with protostars and their outflows is indirectly identified in a significant part of the Serpens Main low-mass star-forming region. Its strength is consistent with the values obtained from the OH and H2O ratios observed with Herschel and compared with models of UV-illuminated shocks. From a chemical viewpoint, the CN to HCN ratio is an excellent tracer of UV fields around low- and intermediate-mass star-forming regions.

AB - Context. Ultraviolet radiation (UV) influences the physics and chemistry of star-forming regions, but its properties and significance in the immediate surroundings of low-mass protostars are still poorly understood.Aims. Our aim is to extend the use of the CN/HCN ratio, already established for high-mass protostars, to the low-mass regime to trace and characterize the UV field around low-mass protostars on similar to 0.6 x 0.6 pc scales.Methods. We present 5' x 5' maps of the Serpens Main Cloud encompassing ten protostars observed with the EMIR receiver at the IRAM 30 m telescope in CN 1-0, HCN 1-0, CS 3-2, and some of their isotopologs. The radiative-transfer code RADEX and the chemical model Nahoon were used to determine column densities of molecules, gas temperature and density, and the UV field strength, G(0).Results. The spatial distribution of HCN and CS are closely correlated with CO 6-5 emission, that traces outflows. The CN emission is extended from the central protostars to their immediate surroundings also tracing outflows, likely as a product of HCN photodissociation. The ratio of CN to HCN total column densities ranges from similar to 1 to 12 corresponding to G(0) approximate to 10(1) -10(3) for gas densities and temperatures typical for outflows of low-mass protostars.Conclusions. UV radiation associated with protostars and their outflows is indirectly identified in a significant part of the Serpens Main low-mass star-forming region. Its strength is consistent with the values obtained from the OH and H2O ratios observed with Herschel and compared with models of UV-illuminated shocks. From a chemical viewpoint, the CN to HCN ratio is an excellent tracer of UV fields around low- and intermediate-mass star-forming regions.

KW - stars: protostars

KW - ISM: jets and outflows

KW - ISM: molecules

KW - ISM: individual objects: Serpens Main

KW - stars: formation

KW - astrochemistry

KW - STAR-FORMING REGIONS

KW - YOUNG STELLAR OBJECTS

KW - J CO OBSERVATIONS

KW - MOLECULAR LINE

KW - SUBMILLIMETER-CONTINUUM

KW - HERSCHEL-PACS

KW - GAS EMISSION

KW - KEY PROGRAM

KW - GOULD BELT

KW - DENSE GAS

U2 - 10.1051/0004-6361/202140833

DO - 10.1051/0004-6361/202140833

M3 - Journal article

VL - 656

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

SN - 0004-6361

M1 - A146

ER -