在A2218中透镜亚毫米星系的新CO探测：探测高红移下LIRG区域的分子气体
New CO detections of lensed submillimeter galaxies in A2218: Probing molecular gas in the LIRG regime at high redshift
摘要：
背景：亚毫米星系（SMG）是遥远的尘埃星系，正在以惊人的速度形成恒星。最近，在理解明亮SMG（即S（850 μ m）> 5 mJy）的性质方面取得了重大进展。较暗的SMG的样本较小，目前正处于通过鉴定研究建立的阶段。目的：我们研究了SMMJ 163555和SMMJ 163541两个SMG在z=1.034和z=3.187处的分子气体含量，非透镜亚毫米通量分别为0.4mJy和6.0mJy。两个SMG都被前景簇A2218引力透镜化。方法：获得SMMJ 163555的CO（2-1）线和SMMJ 163541的CO（3-2）线在3 mm处的IRAM Plateau de Bure干涉测量观察结果。此外，我们还获得了候选者z=4.048 SMMJ 163556的CO（4-3），其无透镜的亚毫米通量为2.7mJy。结果：SMMJ 163555在z=1.0313处检测到CO（2-1），积分谱线强度为1.2 ± 0.2Jy km/s，谱线宽度为410 ± 120 km/s。由此得出气体质量为1.6x10^9 Msun，恒星形成效率估计为440 Lsun/Msun。SMMJ 163541在z=3.1824处检测到CO（3-2），可能在z=3.1883处具有第二分量，积分线强度为1.0 ± 0.1 μ km/s，线宽为280 ± 50 km/s。由此得出气体质量为2.2x10^10 Msun，恒星形成效率估计为1000 Lsun/Msun。对于SMMJ 163556，CO（4-3）在红移范围4.035-4.082内未被检测到，灵敏度为0.15 Jy km/s。结论：我们的CO线观测证实了SMMJ 163555和SMMJ 163541的光学红移。两个星系的CO线光度L '_CO符合L_FIR-L'_CO关系。SMMJ 163555在所有已知红移的SMG中具有最低的FIR光度，并且是少数几个可以在ALMA之前估计其属性的高红移LIRG之一。
英文摘要：
Context: Submillimeter galaxies (SMGs) are distant, dusty galaxies undergoing star formation at prodigious rates. Recently there has been major progress in understanding the nature of the bright SMGs (i.e. S(850um)>5mJy). The samples for the fainter SMGs are small and are currently in a phase of being built up through identification studies. Aims: We study the molecular gas content in two SMGs, SMMJ163555 and SMMJ163541, at z=1.034 and z=3.187 with unlensed submm fluxes of 0.4mJy and 6.0mJy. Both SMGs are gravitationally lensed by the foreground cluster A2218. Methods: IRAM Plateau de Bure Interferometry observations at 3mm were obtained for the lines CO(2-1) for SMMJ163555 and CO(3-2) for SMMJ163541. Additionally we obtained CO(4-3) for the candidate z=4.048 SMMJ163556 with an unlensed submm flux of 2.7mJy. Results: CO(2-1) was detected for SMMJ163555 at z=1.0313 with an integrated line intensity of 1.2+-0.2Jy km/s and a line width of 410+-120 km/s. From this a gas mass of 1.6x10^9 Msun is derived and a star formation efficiency of 440Lsun/Msun is estimated. CO(3-2) was detected for SMMJ163541 at z=3.1824, possibly with a second component at z=3.1883, with an integrated line intensity of 1.0+-0.1 Jy km/s and a line width of 280+-50 km/s. From this a gas mass of 2.2x10^10 Msun is derived and a star formation efficiency of 1000 Lsun/Msun is estimated. For SMMJ163556 the CO(4-3) is undetected within the redshift range 4.035-4.082 down to a sensitivity of 0.15 Jy km/s. Conclusions: Our CO line observations confirm the optical redshifts for SMMJ163555 and SMMJ163541. The CO line luminosity L'_CO for both galaxies is consistent with the L_FIR-L'_CO relation. SMMJ163555 has the lowest FIR luminosity of all SMGs with a known redshift and is one of the few high redshift LIRGs whose properties can be estimated prior to ALMA.
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