Papers - Tanaka, Kunihiko

Energizing Star Formation: The Cosmic Ray Ionization Rate in NGC 253 Derived From ALCHEMI Measurements of H$_3$O$^+$ and SO

Holdship, Jonathan ; Mangum, Jeffrey G. ; Viti, Serena ; Behrens, Erica ; Harada, Nanase ; Martín, Sergio ; Sakamoto, Kazushi ; Muller, Sebastien ; Tanaka, Kunihiko ; Nakanishi, Kouichiro ; Herrero-Illana, Rubén ; Yoshimura, Yuki ; Aladro, Rebeca ; Colzi, Laura ; Emig, Kimberly L. ; Henkel, Christian ; Nishimura, Yuri ; Rivilla, Víctor M. ; van der Werf, Paul P.

The Astrophysical Journal 931   89 2022.06

Research paper (scientific journal), Joint Work, Accepted

First extragalactic detection of a phosphorus-bearing molecule with ALCHEMI: Phosphorus nitride (PN)

Haasler, D. search by orcid ; Rivilla, V. M. ; Martín, S. ; Holdship, J. ; Viti, S. ; Harada, N. ; Mangum, J. ; Sakamoto, K. ; Muller, S. ; Tanaka, K. ; Yoshimura, Y. ; Nakanishi, K. ; Colzi, L. search by orcid ; Hunt, L. search by orcid ; Emig, K. L. ; Aladro, R. ; Humire, P. ; Henkel, C. ; van der Werf, P.

Astronomy & Astrophysics (Astronomy and Astrophysics)  659   158 2022.03

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00046361

　View Summary

Context. Phosphorus (P) is a crucial element for life given its central role in several biomolecules. P-bearing molecules have been discovered in different regions of the Milky Way, but not yet towards an extragalactic environment. Aims. We searched for P-bearing molecules outside the Milky Way towards the nearby starburst Galaxy NGC 253. Methods. Using observations from the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI) project, we used the MAdrid Data CUBe Analysis package to model the emission of P-bearing molecules assuming local thermodynamic equilibrium (LTE) conditions. We also performed a non-LTE analysis using SpectralRadex. Results. We report the detection of a P-bearing molecule, phosphorus nitride (PN), for the first time in an extragalactic environment, towards two giant molecular clouds (GMCs) of NGC 253. The LTE analysis yields total PN beam-averaged column densities N = (1.20 ± 0.09) - 1013 cm-2 and N = (6.5 ± 1.6) - 1012 cm-2, which translate into abundances with respect to H2 of = (8.0 ± 1.0) - 10-12 and = (4.4 ± 1.2) - 10-12. We derived a low excitation temperature of Tex = (4.4 ± 1.3) K towards the GMC with the brightest PN emission, which indicates that PN is sub-thermally excited. The non-LTE analysis results in column densities consistent with the LTE values. We also searched for other P-bearing molecules (PO, PH3, CP, and CCP), and upper limits were derived. The derived PO/PN ratios are < 1.3 and < 1.7. The abundance ratio between PN and the shock-tracer SiO derived towards NGC 253 follows the same trend previously found towards Galactic sources. Conclusions. Comparison of the observations with chemical models indicates that the derived molecular abundances of PN in NGC 253 can be explained by shock-driven chemistry followed by cosmic-ray-driven photochemistry.

• Access to Document (DOI)

Starburst Energy Feedback Seen through HCO⁺/HOC⁺Emission in NGC 253 from ALCHEMI

Harada N., Martín S., Mangum J.G., Sakamoto K., Muller S., Tanaka K., Nakanishi K., Herrero-Illana R., Yoshimura Y., Mühle S., Aladro R., Colzi L., Rivilla V.M., Aalto S., Behrens E., Henkel C., Holdship J., Humire P.K., Meier D.S., Nishimura Y., Van Der Werf P.P., Viti S.

Astrophysical Journal (Astrophysical Journal)  923 ( 1 )  2021.12

ISSN  0004637X

　View Summary

Molecular abundances are sensitive to the UV photon flux and cosmic-ray ionization rate. In starburst environments, the effects of high-energy photons and particles are expected to be stronger. We examine these astrochemical signatures through multiple transitions of HCO+ and its metastable isomer HOC+ in the center of the starburst galaxy NGC 253 using data from the Atacama Large Millimeter/submillimeter Array large program ALMA Comprehensive High-resolution Extragalactic Molecular inventory. The distribution of the HOC+(1-0) integrated intensity shows its association with "superbubbles,"cavities created either by supernovae or expanding H ii regions. The observed HCO+/HOC+ abundance ratios are ∼10-150, and the fractional abundance of HOC+ relative to H2 is ∼1.5 × 10-11-6 × 10-10, which implies that the HOC+ abundance in the center of NGC 253 is significantly higher than in quiescent spiral arm dark clouds in the Galaxy and the Galactic center clouds. Comparison with chemical models implies either an interstellar radiation field of G 0 ⪆ 103 if the maximum visual extinction is ⪆5, or a cosmic-ray ionization rate of ζ ⪆ 10-14 s-1 (3-4 orders of magnitude higher than that within clouds in the Galactic spiral arms) to reproduce the observed results. From the difference in formation routes of HOC+, we propose that a low-excitation line of HOC+ traces cosmic-ray dominated regions, while high-excitation lines trace photodissociation regions. Our results suggest that the interstellar medium in the center of NGC 253 is significantly affected by energy input from UV photons and cosmic rays, sources of energy feedback.

• Access to Document (DOI)

ALCHEMI, an ALMA Comprehensive High-resolution Extragalactic Molecular Inventory: Survey presentation and first results from the ACA array

Martín S., Mangum J.G., Harada N., Costagliola F., Sakamoto K., Muller S., Aladro R., Tanaka K., Yoshimura Y., Nakanishi K., Herrero-Illana R., Mühle S., Aalto S., Behrens E., Colzi L., Emig K.L., Fuller G.A., García-Burillo S., Greve T.R., Henkel C., Holdship J., Humire P., Hunt L., Izumi T., Kohno K., König S., Meier D.S., Nakajima T., Nishimura Y., Padovani M., Rivilla V.M., Takano S., Van Der Werf P.P., Viti S., Yan Y.T.

Astronomy and Astrophysics (Astronomy and Astrophysics)  656 2021.12

Research paper (scientific journal), Accepted,  ISSN  00046361

　View Summary

Context. The interstellar medium is the locus of physical processes affecting the evolution of galaxies which drive or are the result of star formation activity, supermassive black hole growth, and feedback. The resulting physical conditions determine the observable chemical abundances that can be explored through molecular emission observations at millimeter and submillimeter wavelengths. Aims. Our goal is to unveiling the molecular richness of the central region of the prototypical nearby starburst galaxy NGC 253 at an unprecedented combination of sensitivity, spatial resolution, and frequency coverage. Methods. We used the Atacama Large Millimeter/submillimeter Array (ALMA), covering a nearly contiguous 289 GHz frequency range between 84.2 and 373.2 GHz, to image the continuum and spectral line emission at 1.6″(∼28 pc) resolution down to a sensitivity of 30 - 50 mK. This article describes the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI) large program. We focus on the analysis of the spectra extracted from the 15″ (∼255 pc) resolution ALMA Compact Array data. Results. We modeled the molecular emission assuming local thermodynamic equilibrium with 78 species being detected. Additionally, multiple hydrogen and helium recombination lines are identified. Spectral lines contribute 5 to 36% of the total emission in frequency bins of 50 GHz. We report the first extragalactic detections of C2H5OH, HOCN, HC3HO, and several rare isotopologues. Isotopic ratios of carbon, oxygen, sulfur, nitrogen, and silicon were measured with multiple species. Concluison. Infrared pumped vibrationaly excited HCN, HNC, and HC3N emission, originating in massive star formation locations, is clearly detected at low resolution, while we do not detect it for HCO+. We suggest high temperature conditions in these regions driving a seemingly "carbon-rich"chemistry which may also explain the observed high abundance of organic species close to those in Galactic hot cores. The Lvib/LIR ratio was used as a proxy to estimate a 3% contribution from the proto super star cluster to the global infrared emission. Measured isotopic ratios with high dipole moment species agree with those within the central kiloparsec of the Galaxy, while those derived from 13C/18O are a factor of five larger, confirming the existence of multiple interstellar medium components within NGC 253 with different degrees of nucleosynthesis enrichment. The ALCHEMI data set provides a unique template for studies of star-forming galaxies in the early Universe.

• Access to Document (DOI)

Starburst Energy Feedback Seen Through HCO$^+$/HOC$^+$ Emission in NGC 253 from ALCHEMI

Nanase Harada, Sergio Martín, Jeffrey G. Mangum, Kazushi Sakamoto, Sebastien Muller, Kunihiko Tanaka, Kouichiro Nakanishi, Rubén Herrero-Illana, Yuki Yoshimura, Stefanie Mühle, Rebeca Aladro, Laura Colzi, Víctor M. Rivilla, Susanne Aalto, Erica Behrens, Christian Henkel, Jonathan Holdship, P. K. Humire, David S. Meier, Yuri Nishimura, Paul P. van der Werf, Serena Viti

Astrophysical Journal 923   24 2021.12

Joint Work, Accepted

Clustered Star Formation in the Center of NGC 253 Contributes to Driving the Ionized Nuclear Wind

Mills E.A.C., Gorski M., Emig K.L., Bolatto A.D., Levy R.C., Leroy A.K., Ginsburg A., Henshaw J.D., Zschaechner L.K., Veilleux S., Tanaka K., Meier D.S., Walter F., Krieger N., Ott J.

Astrophysical Journal (Astrophysical Journal)  919 ( 2 )  2021.10

Research paper (scientific journal), Accepted,  ISSN  0004637X

　View Summary

We present new 3 mm observations of the ionized gas toward the nuclear starburst in the nearby (D ∼ 3.5 Mpc) galaxy NGC 253. With ALMA, we detect emission from the H40α and He40α lines in the central 200 pc of this galaxy on spatial scales of ∼4 pc. The recombination line emission primarily originates from a population of approximately a dozen embedded super star clusters in the early stages of formation. We find that emission from these clusters is characterized by electron temperatures ranging from 7000 to 10,000 K and measures an average singly ionized helium abundance Y + = 0.25 0.06, both of which are consistent with values measured for H ii regions in the center of the Milky Way. We also report the discovery of unusually broad line width recombination line emission originating from seven of the embedded clusters. We suggest that these clusters contribute to the launching of the large-scale hot wind observed to emanate from the central starburst. Finally, we use the measured recombination line fluxes to improve the characterization of overall embedded cluster properties, including the distribution of cluster masses and the fractional contribution of the clustered star formation to the total starburst, which we estimate is at least 50%.

• Access to Document (DOI)

Atomic Carbon in the Central Molecular Zone of the Milky Way : Possible Cosmic–ray Induced Chemistry or Time–dependent Chemistry Associated with SNR Sagittarius A East

Kunihiko Tanaka, Makoto Nagai, Kazuhisa Kamegai

Astrophysical Journal (IOP publishing )  915 ( 2 ) 79 2021.07

Research paper (scientific journal), Joint Work, Lead author, Accepted,  ISSN  0004637X

　View Summary

Atomic carbon (C0), being one of the most abundant atomic/molecular species observed in dense molecular gas, is potentially a good tracer of molecular gas mass in many chemical/physical environments, though the variation in C0 abundance outside the Galactic disk region is not yet fully known. This paper presents a wide-field 500 GHz [C i] map of the Galactic central molecular zone (CMZ) obtained with the ASTE 10 m telescope. Principal component analysis and non-LTE multi-transition analysis have shown that [C i] emission predominantly originates from the low-excitation gas component with a temperature of 20-50 K and density of ∼103 cm-3, whereas C0 abundance is likely suppressed in the high-excitation gas component. The average N(C0)/N(CO) abundance ratio in the CMZ is 0.3-0.4, which is 2-3 times that in the Galactic disk. The N(C0)/N(CO) ratio increases to 0.7 in the innermost 10 pc region and to ∼2 in the circumnuclear disk. We discovered C0-rich regions distributed in a ring shape encircling the supernova remnant (SNR) Sgr A East, indicating that the C0 enrichment in the central 10 pc region is a consequence of a molecular cloud-SNR interaction. In the 15 atoms/molecules included in principal component analysis, CN is the only other species that increases in the [C i]-bright ring. The origin of the [C i]-bright ring is likely a cosmic-ray-dominated region created by low-energy cosmic-ray particles accelerated by Sgr A East or primitive molecular gas collected by the SNR in which the conversion from C0 to CO has not reached equilibrium.

• Access to Document (DOI)

The Distribution and Origin of C$_2$H in NGC 253 from ALCHEMI

J. Holdship, S. Viti, S. Martín, N. Harada, J. Mangum, K. Sakamoto, S. Muller, K. Tanaka, Y. Yoshimura, K. Nakanishi, R. Herrero-Illana, S. Mühle, R. Aladro, L. Colzi, K. L. Emig, S. García-Burillo, C. Henkel, P. Humire, D. S. Meier, V. M. Rivilla, P. van der Werf

A&A 654, A55 (2021) (Astronomy and Astrophysics)  654 2021.07

Research paper (scientific journal), Joint Work,  ISSN  00046361

　View Summary

Observations of chemical species can provide an insight into the physical
conditions of the emitting gas but it is important to understand how their
abundances and excitation vary within different heating environments. C$_2$H is
a molecule typically found in PDR regions of our own Galaxy but there is
evidence to suggest it also traces other regions undergoing energetic
processing in extragalactic environments. As part of the ALCHEMI ALMA large
program, the emission of C$_2$H in the central molecular zone of the nearby
starburst galaxy NGC 253 was mapped at 1.6 " (28 pc) resolution and
characterized to understand its chemical origins. Spectral modelling of the
N=1-0 through N=4-3 rotational transitions of C$_2$H was used to derive the
C$_2$H column densities towards the dense clouds in NGC 253. Chemical
modelling, including PDR, dense cloud, and shock models were then used to
investigate the chemical processes and physical conditions that are producing
the molecular emission. We find high C$_2$H column densities of $\sim 10^{15}
cm^{-3}$ detected towards the dense regions of NGC 253. We further find that
these column densities cannot be reproduced by assuming that the emission
arises from the PDR regions at the edge of the clouds. Instead, we find that
the C$_2$H abundance remains high even in the high visual extinction interior
of these clouds and that this is most likely caused by a high cosmic-ray
ionization rate.


• Access to Document (DOI)

HCN J = 4–3, HNC J = 1–0, H 13 CN J = 1–0, and HC 3 N J = 10–9 Maps of the Galactic Center Region. II: Physical Properties of Dense Gas Clumps and Propbability of Star Formation

Kunihiko Tanaka, Makoto Nagai, Kazuhisa Kamegai, Takahiro Iino, Takeshi Sakai

Astrophysical Journal (IOP publishing)  903   111 2020.11

Research paper (scientific journal), Joint Work, Accepted

HCN J = 4–3, HNC J = 1–0, H 13 CN J = 1–0, and HC 3 N J = 10–9 Maps of the Galactic Center Region. I. Spatially Resolved Measurements of Physical Conditions and Chemical Composition

TANAKA Kunihiko Makoto Nagai Kazuhisa Kamegai Takahiro Iino Takeshi Sakai

The Astrophysical Journal Supplement Series (IOP)  236 ( 2 ) 40 2018.06

Research paper (scientific journal), Joint Work, Accepted

ALMA Images of the Host Cloud of the Intermediate-mass Black Hole Candidate CO-0.40-0.22$^*$: No Evidence for Cloud--Black Hole Interaction, but Evidence for a Cloud--Cloud Collision

TANAKA Kunihiko

Astrophysical Journal (IOP publishing)  859 ( 2 ) 86 - 100 2018.06

Research paper (scientific journal), Accepted,  ISSN  0004637X

　View Summary

This paper reports a reanalysis of archival ALMA data of the high velocity(-width) compact cloud CO-0.40-0.22, which has recently been hypothesized to host an intermediate-mass black hole (IMBH). If beam-smearing effects, difference in beam sizes among frequency bands, and Doppler shift due to the motion of the Earth are considered accurately, none of the features reported as evidence for an IMBH in previous studies are confirmed in the reanalyzed ALMA images. Instead, through analysis of the position-velocity structure of the HCN J = 3-2 data cube, we have found kinematics typical of a cloud-cloud collision (CCC), namely, two distinct velocity components bridged by broad emission features with elevated temperatures and/or densities. One velocity component has a straight filamentary shape with approximately constant centroid velocities along its length but with a steep, V-shaped velocity gradient across its width. This contradicts the IMBH scenario but is consistent with a collision between two dissimilar-sized clouds. From a non-LTE analysis of the multitransition methanol lines, the volume density of the post-shock gas has been measured to be 106 cm-3, indicating that the CCC shock can compress gas in a short timescale to densities typical of star-forming regions. Evidence for star formation has not been found, possibly because the cloud is in an early phase of CCC-triggered star formation or because the collision is nonproductive.

• Access to Document (DOI)

A statistical study of giant molecular clouds traced by 13CO, C18O, CS, and CH3OH in the disk of NGC 1068 based on ALMA observations

Tosaki, Tomoka; Kohno, Kotaro; Harada, Nanase; Tanaka, Kunihiko; Egusa, Fumi; Izumi, Takuma; Takano, Shuro; Nakajima, Taku; Taniguchi, Akio; Tamura, Yoichi

Publications of the Astronomical Society of Japan (Oxford University Press on behalf of the Astronomical Society of Japan)   2017.01

Research paper (scientific journal), Joint Work, Accepted

Search for the CO-dark Mass in the Central Molecular Zone by using the ASTE 10-m Telescope

TANAKA Kunihiko

The Multi-Messenger Astrophysics of the Galactic Centre, Proceedings of the International Astronomical Union, IAU Symposium    107 - 110 2017.01

Research paper (international conference proceedings), Single Work

Physical Contact between the +20 km s^{-1} Cloud and the Galactic Circumnuclear Disk

Takekawa, Shunya; Oka, Tomoharu; Tanaka, Kunihiko

The Astrophysical Journal, 834 ( 2 ) 121 2017.01

Accepted

CO-0.30-0.07: a Peculiar Molecular Clump with an Extremely Broad Velocity Width in the Central Molecular Zone of the Milky Way

TANAKA Kunihiko

The Astrophysical Journal (IOP publishing)  806   130 - 142 2015.06

Research paper (scientific journal), Joint Work, Accepted

CO-0.30-0.07: A Candidate Site of Collision-induced Massive Star Formation in the Milky Way's Central Molecular Zone

TANAKA Kunihiko

Conditions and Impact of Star Formation. Edited by R. Simon, R. Schaaf and J. Stutzki. EAS Publications Series 75-76   181 - 184 2015.05

Research paper (international conference proceedings), Single Work

Dense Molecular Clumps Associated with the Large Magellanic Cloud Supergiant Shells LMC 4 and LMC 5

Fujii, Kosuke; Minamidani, Tetsuhiro; Mizuno, Norikazu; Onishi, Toshikazu; Kawamura, Akiko; Muller, Erik; Dawson, Joanne; Tatematsu, Ken'ichi; Hasegawa, Tetsuo; Tosaki, Tomoka; Miura, Rie E.; Muraoka, Kazuyuki; Sakai, Takeshi; Tsukagoshi, Takashi; Tanaka, Kunihiko; Ezawa, Hajime; Fukui, Yasuo

The Astrophysical Journal 796 ( 2 ) 123 - 141 2014.12

Research paper (scientific journal), Joint Work, Accepted

Millimeter-wave Spectral Line Surveys toward the Galactic Circumnuclear Disk and Sgr A*

Takekawa, Shunya; Oka, Tomoharu; Tanaka, Kunihiko; Matsumura, Shinji; Miura, Kodai; Sakai, Daisuke

The Astrophysical Journal Supplement 214 ( 1 )  2014.09

Research paper (scientific journal), Joint Work, Accepted

Millimeter-wave Molecular Line Observations of the Tornado Nebula

Sakai, D.; Oka, T.; Tanaka, K.; Matsumura, S.; Miura, K.; Takekawa, S.

The Astrophysical Journal 791 ( 1 )  2014.08

Research paper (scientific journal), Joint Work, Accepted

High Velocity Compact Clouds in the Sagittarius C Region

TTanaka, Kunihiko; Oka, Tomoharu; Matsumura, Shinji; Nagai, Makoto; Kamegai, Kazuhisa

Astrophysical Journal 783   62-71 2014.03

Research paper (scientific journal), Joint Work, Accepted