ترغب بنشر مسار تعليمي؟ اضغط هنا

ALMA observations of molecular gas in the host galaxy of AT2018cow

91   0   0.0 ( 0 )
 نشر من قبل Kana Morokuma-Matsui
 تاريخ النشر 2019
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

We investigate the molecular gas in, and star-formation properties of, the host galaxy (CGCG 137-068) of a mysterious transient, AT2018cow, at kpc and larger scales, using archival band-3 data from the Atacama Large Millimeter/submillimeter Array (ALMA). AT2018cow is the nearest Fast-Evolving Luminous Transient (FELT), and this is the very first study unveiling molecular-gas properties of FELTs. The achieved rms and beam size are 0.21 mJy beam$^{-1}$ at a velocity resolution of $40$ km s$^{-1}$ and $3.66times2.71$ ($1.1~{rm kpc} times 0.8~{rm kpc}$), respectively. CO($J$=1-0) emission is successfully detected. The total molecular gas mass inferred from the CO data is $(1.85pm0.04)times10^8$ M$_odot$ with the Milky Way CO-to-H$_2$ conversion factor. The H$_2$ column density at the AT2018cow site is estimated to be $8.6times10^{20}$ cm$^{-2}$. The ALMA data reveal that (1) CGCG 137-068 is a normal star-forming (SF) dwarf galaxy in terms of its molecular gas and star-formation properties and (2) AT2018cow is located between a CO peak and a blue star cluster. These properties suggest on-going star formation and favor the explosion of a massive star as the progenitor of AT2018cow. We also find that CGCG 137-068 has a solar or super-solar metallicity. If the metallicity of the other FELT hosts is not higher than average, then some property of SF dwarf galaxies other than metallicity may be related to FELTs.



قيم البحث

اقرأ أيضاً

We present the results of CO interferometric observations of the southern elliptical galaxy NGC3557 with ALMA. We have detected both the CO(1-0) emission line and a relatively strong continuum at 3mm. The continuum shows a flat-spectrum central unres olved source (at our angular resolution of 0.7arcsec) and two jets, associated with the larger scale emission observed at lower frequencies. The molecular gas in NGC3557 appears to be concentrated within 250 pc of the center, and shows evidence of organized rotation along the same axis as the stellar component and the symmetry axis of the nuclear dust absorption reported in the literature. We obtained M$_{H_2}$=(9.0$pm$2.0)x10$^7$ M$_odot$ of molecular gas, which has an average CO(2-1) to CO(1-0) line ratio of 0.7, which is relatively high when compared with the values reported in the literature for bona-fide ellipticals observed with single-dish telescopes. NGC3557 shows further a high excitation peak (i.e., CO(2-1)/CO(1-0) ~ 1.1$pm$0.3 offset 0.7 arcsec from the center, which appears to be associated with a region of higher velocity dispersion that does not share the overall rotation pattern of the molecular gas, but aligned with the radio jet. The molecular gas disk in this object appears to be stable to local gravitational instabilities.
We present the results of CO(1-0) and CO(4-3) observations of the host galaxy of a long-duration gamma-ray burst GRB080207 at z = 2.0858 by using the Karl G. Jansky Very Large Array and the Atacama Large Millimeter/submillimeter Array. The host is de tected in CO(1-0) and CO(4-3), becoming the first case for a GRB host with more than two CO transitions detected combined with CO(2-1) and CO(3-2) in the literature. Adopting a metallicity-dependent CO-to-H2 conversion factor, we derive a molecular gas mass of Mgas = 8.7 x 10^10 Modot, which places the host in a sequence of normal star-forming galaxies in a Mgas-star-formation rate (SFR) plane. A modified blackbody fit to the far-infrared--millimeter photometry results in a dust temperature of 37 K and a dust mass of Mdust = 1.5 x 10^8 Modot. The spatially-resolving CO(4-3) observations allow us to examine the kinematics of the host. The CO velocity field shows a clear rotation and is reproduced by a rotation-dominated disk model with a rotation velocity of 350 km/s and a half-light radius of 2.4 kpc. The CO spectral line energy distribution derived from the four CO transitions is similar to that of starburst galaxies, suggesting a high excitation condition. Comparison of molecular gas properties between the host and normal (main-sequence) galaxies at similar redshifts shows that they share common properties such as gas mass fraction, gas depletion timescale, gas-to-dust ratio, location in the Mgas-SFR (or surface density) relation, and kinematics, suggesting that long-duration GRBs can occur in normal star-forming environments at z ~ 2.
112 - Gan Luo , Di Li , Ningyu Tang 2019
Carbon-bearing molecules, particularly CO, have been widely used as tracers of molecular gas in the interstellar medium (ISM). In this work, we aim to study the properties of molecules in diffuse, cold environments, where CO tends to be under-abundan t and/or sub-thermally excited. We performed one of the most sensitive (down to $mathrm{tau_{rms}^{CO} sim 0.002}$ and $mathrm{tau_{rms}^{HCO^+} sim 0.0008}$) sub-millimeter molecular absorption line observations towards 13 continuum sources with the ALMA. CO absorption was detected in diffuse ISM down to $mathrm{A_v< 0.32,mag}$ and hcop was down to $mathrm{A_v < 0.2,mag}$, where atomic gas and dark molecular gas (DMG) starts to dominate. Multiple transitions measured in absorption toward 3C454.3 allow for a direct determination of excitation temperatures $mathrm{T_{ex}}$ of 4.1,K and 2.7,K, for CO and for hcop, respectively, which are close to the cosmic microwave background (CMB) and provide explanation for their being undercounted in emission surveys. A stronger linear correlation was found between $mathrm{N_{HCO^+}}$ and $mathrm{N_{H_2}}$ (Pearson correlation coefficient P $sim$ 0.93) than that of $mathrm{N_{CO}}$ and $mathrm{N_{H_2}}$ (P $sim$ 0.33), suggesting hcop being a better tracer of H$_2$ than CO in diffuse gas. The derived CO-to-h2 conversion factor (the CO X-factor) of (14 $pm$ 3) $times$ 10$^{20}$ cm$^{-2}$ (K kms)$^{-1}$ is approximately 6 times larger than the average value found in the Milky Way.
We present the results of CO observations toward 14 host galaxies of long-duration gamma-ray bursts (GRBs) at z = 0.1-2.5 by using the Atacama Large Millimeter/submillimeter Array. We successfully detected CO(3-2) or CO(4-3) emission in eight hosts ( z = 0.3-2), which more than doubles the sample size of GRB hosts with CO detection. The derived molecular gas mass is $M_{rm gas} = (0.2-6) times 10^{10}$ $M_{odot}$ assuming metallicity-dependent CO-to-H$_2$ conversion factors. By using the largest sample of GRB hosts with molecular gas estimates (25 in total, of which 14 are CO-detected) including results from the literature, we compared molecular gas properties with those of other star-forming galaxies (SFGs). The GRB hosts tend to have a higher molecular gas mass fraction ($mu_{rm gas}$) and a shorter gas depletion timescale ($t_{rm depl}$) as compared with other SFGs at similar redshifts especially at $z lesssim 1$. This could be a common property of GRB hosts or an effect introduced by the selection of targets which are typically above the main-sequence line. To eliminate the effect of selection bias, we analyzed $mu_{rm gas}$ and $t_{rm depl}$ as a function of the distance from the main-sequence line ($delta$MS). We find that the GRB hosts follow the same scaling relations as other SFGs, where $mu_{rm gas}$ increases and $t_{rm depl}$ decreases with increasing $delta {rm MS}$. No molecular gas deficit is observed when compared to other SFGs of similar SFR and stellar mass. These findings suggest that the same star-formation mechanism is expected to be happening in GRB hosts as in other SFGs.
We report new, $sim$1000 AU spatial resolution observations of 225 GHz dust continuum emission towards the OB cluster-forming molecular clump G33.92+0.11. On parsec scales, this molecular clump presents a morphology with several arm-like dense gas st ructures surrounding the two central massive ($gtrsim$100 $M_{odot}$) cores. From the new, higher resolution observations, we identified 28 localized, spatially compact dust continuum emission sources, which may be candidates of young stellar objects. Only one of them is not embedded within known arm-like (or elongated) dense gas structures. The spatial separations of these compact sources can be very well explained by Jeans lengths. We found that G33.92+0.11 may be consistently described by a marginally centrifugally supported, Toomre unstable accretion flow which is approximately in a face-on projection. The arm-like overdensities are natural consequence of the Toomre instability, which can fragment to form young stellar objects in shorter time scales than the timescale of the global clump contraction. On our resolved spatial scales, there is not yet evidence that the fragmentation is halted by turbulence, magnetic field, or stellar feedback.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا