Using the IRAM 30-m telescope, CN and CO isotopologues have been measured
toward the central regions of the nearby starburst galaxy NGC253 and the
prototypical ultraluminous infrared galaxy Mrk231. In NGC253, the 12C/13C ratio
is 40+-10. Assuming that the ratio also holds for the CO emitting gas, this
yields 16O/18O = 145+-36 and 16O/17O = 1290+-365 and a 32S/34S ratio close to
that measured for the local interstellar medium (20-25). No indication for
vibrationally excited CN is found. Peak line intensity ratios between NGC253
and Mrk231 are ~100 for 12C16O and 12C18O J=1-0, while the ratio for 13C16O
J=1-0 is ~250. This and similar 13CO and C18O line intensities in the J=1-0 and
2-1 transitions of Mrk231 suggest 12C/13C ~ 100 and 16O/18O ~ 100, in agreement
with values obtained for the less evolved ultraluminous merger Arp220. Also
accounting for other extragalactic data, 12C/13C ratios appear to vary over a
full order of magnitude, from >100 in ultraluminous high redshift galaxies to
~100 in more local such galaxies to ~40 in weaker starbursts not undergoing a
large scale merger to 25 in the Central Molecular Zone of the Milky Way. With
12C being predominantly synthesized in massive stars, while 13C is mostly
ejected by longer lived lower mass stars at later times, this is qualitatively
consistent with our results of decreasing carbon isotope ratios with time and
rising metallicity. It is emphasized, however, that both infall of poorly
processed material, initiating a nuclear starburst, as well as the ejecta from
newly formed massive stars (in particular in case of a top-heavy stellar
initial mass function) can raise the carbon isotope ratio for a limited amount
of time.Comment: Accepted by Astronomy & Astrophysics, 6 figures, 4 table

Aalto, S.

Aladro, R.

Ao, Y.

Asiri, H.

Danielson, A. L. R.

Garcia-Burillo, S.

Harada, N.

Henkel, C.

Impellizzeri, C. M. V.

Martin, S.

Mauersberger, R.

Papadopoulos, P. P.

English

arXiv

C. Henkel

H. Asiri

Y. Ao

S. Aalto

A. L. R. Danielson

P. P. Papadopoulos

S. García-Burillo

R. Aladro

C. M. V. Impellizzeri

R. Mauersberger

S. Martín

N. Harada

Crossref

Astronomy and Astrophysics

Carbon and oxygen isotope ratios in starburst galaxies: New data from NGC 253 and Mrk 231 and their implications

Carbon and oxygen isotope ratios are excellent measures of nuclear processing, but few such data have been taken toward extragalactic targets so far. Therefore, using the IRAM 30-m telescope, CN and CO isotopologues have been measured toward the nearby starburst galaxy NGC 253 and the prototypical ultraluminous infrared galaxy Mrk 231. Toward the center of NGC 253, the CN and (CN)-C-13 N = 1 -> 0 lines indicate no significant deviations from expected local thermodynamical equilibrium after accounting for moderate saturation effects (10 and 25%) in the two detected spectral components of the main species. Including calibration uncertainties, which dominate the error budget, the C-12/C-13 ratio becomes 40 +/- 10. This is larger than the ratio in the central molecular zone of the Galaxy, suggesting a higher infall rate of poorly processed gas toward the central region. Assuming that the ratio also holds for the CO emitting gas, this yields O-16/O-18 = 145 +/- 36 and O-16/O-17 = 1290 +/- 365 and a S-32/S-34 ratio close to the one measured for the local interstellar medium (2025). No indication of vibrationally excited CN is found in the lower frequency fine structure components of the N = 1 -> 0 and 2 -> 1 transitions at rms noise levels of 3 and 4 mK (15 and 20 mJy) in 8.5 km s-1 wide channels. Peak line intensity ratios between NGC 253 and Mrk 231 are similar to 100 for (CO)-C-12-O-16 and (CO)-C-12-O-18 J = 1 -> 0, while the ratio for (CO)-C-13-O-16 J = 1 -> 0 is similar to 250. This and similar (CO)-C-13 and (CO)-O-18 line intensities in the J = 1 -> 0 and 2 -> 1 transitions of Mrk 231 suggest C-12/C-13 similar to 100 and O-16/O-18 similar to 100, in agreement with values obtained for the less evolved ultraluminous merger Arp 220. Also, when accounting for other (scarcely available) extragalactic data, C-12/C-13 ratios appear to vary over a full order of magnitude, from >100 in ultraluminous high redshift galaxies to similar to 100 in more local such galaxies to similar to 40 in weaker starbursts that are not undergoing a large scale merger to 25 in the central molecular zone of the Milky Way. With C-12 being predominantly synthesized in massive stars, while C-13 is mostly ejected by longer lived lower mass stars at later times, this is qualitatively consistent with our results of decreasing carbon isotope ratios with time and rising metallicity. It is emphasized, however, that both infall of poorly processed material, initiating a nuclear starburst, and the ejecta from newly formed massive stars (in particular in the case of a top-heavy stellar initial mass function) can raise the carbon isotope ratio for a limited amount of time

Henkel, C.,

Asiri, H.,

Ao, Y.,

Aalto, Susanne,

Danielson, A. L. R.,

Papadopoulos, P. P.,

Burillo, S. G.,

Aladro, Rebeca,

Impellizzeri, C. M. V.,

Mauersberger, R.,

Martin, S.,

Harada, N.,

Swepub

Carbon and oxygen isotope ratios in starburst galaxies: New data from NGC 253 and Mrk 231 and their implications [Elektronisk resurs]

Aalto, Susanne

Burillo, S. G.

Aladro, Rebeca

Chalmers Research

Carbon and oxygen isotope ratios are excellent measures of nuclear processing, but few
          such data have been taken toward extragalactic targets so far. Therefore, using the IRAM
          30-m telescope, CN and CO isotopologues have been measured toward the nearby starburst
          galaxy NGC 253 and the prototypical ultraluminous infrared galaxy Mrk 231. Toward the
          center of NGC 253, the CN and 13CN N = 1 → 0 lines indicate no significant deviations
          from expected local thermodynamical equilibrium after accounting for moderate saturation
          effects (10 and 25%) in the two detected spectral components of the main species.
          Including calibration uncertainties, which dominate the error budget, the 12C/13C ratio becomes
            40 ± 10. This is larger than
          the ratio in the central molecular zone of the Galaxy, suggesting a higher infall rate of
          poorly processed gas toward the central region. Assuming that the ratio also holds for the
          CO emitting gas, this yields 16O/18O = 145 ± 36 and 16O/17O = 1290 ± 365 and a 32S/34S ratio close to the one measured for the local
          interstellar medium (20–25). No indication of vibrationally excited CN is found in the
          lower frequency fine structure components of the N = 1 → 0 and
            2 → 1 transitions at rms
          noise levels of 3 and 4 mK (15 and 20 mJy) in 8.5 km s-1 wide channels. Peak line
          intensity ratios between NGC 253 and Mrk 231 are ~100 for 12C16O and 12C18O J = 1 → 0, while the ratio
          for 13C16O J = 1 → 0 is ~250. This and similar 13CO and C18O line intensities in the
            J = 1 → 0
          and 2 → 1 transitions of Mrk
          231 suggest 12C/13C ~ 100 and 16O/18O ~ 100, in agreement with values obtained for the less evolved
          ultraluminous merger Arp 220. Also, when accounting for other (scarcely available)
          extragalactic data, 12C/13C ratios appear to vary over a full order of magnitude,
          from >100 in ultraluminous high redshift galaxies to
            ~100 in more local such
          galaxies to ~40 in weaker
          starbursts that are not undergoing a large scale merger to 25 in the central molecular
          zone of the Milky Way. With 12C being predominantly synthesized in massive stars, while
            13C is mostly
          ejected by longer lived lower mass stars at later times, this is qualitatively consistent
          with our results of decreasing carbon isotope ratios with time and rising metallicity. It
          is emphasized, however, that both infall of poorly processed material, initiating a
          nuclear starburst, and the ejecta from newly formed massive stars (in particular in the
          case of a top-heavy stellar initial mass function) can raise the carbon isotope ratio for
          a limited amount of time

EDP Sciences OAI-PMH repository (1.2.0)

Carbon and oxygen isotope ratios in starburst galaxies: New
          data from NGC 253 and Mrk 231 and their implications

Chalmers Publication Library