分类： 天文学 >> 天文学 提交时间： 2023-02-19
Sean D. Johnson
Joop Schaye
Gregory L. Walth
Jennifer I-Hsiu Li
Gwen C. Rudie
Hsiao-Wen Chen
Mandy C. Chen
Benoît Epinat
Massimo Gaspari
Sebastiano Cantalupo
Wolfram Kollatschny
Zhuoqi
Liu
Sowgat Muzahid
摘要： We report the discovery of giant (50-100 kpc) [O II] emitting nebulae with the Multi-Unit Spectroscopic Explorer (MUSE) in the field of TXS 0206-048, a luminous quasar at z=1.13. Down-the-barrel UV spectra of the quasar show absorption at velocities coincident with those of the extended nebulae, enabling new insights into inflows and outflows around the quasar host. One nebula exhibits a filamentary morphology extending over 120 kpc from the halo toward the quasar and intersecting with another nebula surrounding the quasar host with a radius of 50 kpc. This is the longest cool filament observed to-date and arises at higher redshift and in a less massive system than those in cool-core clusters. The filamentary nebula has line-of-sight velocities >300 km/s from nearby galaxies but matches that of the nebula surrounding the quasar host where they intersect, consistent with accretion of cool inter- or circum-galactic medium or cooling hot halo gas. The kinematics of the nebulae surrounding the quasar host are unusual and complex, with redshifted and blueshifted spiral-like structures. The emission velocities at 5-10 kpc from the quasar match those of inflowing absorbing gas observed in UV spectra of the quasar. Together, the extended nebulae and associated redshifted absorption represent a compelling case of cool, filamentary gas accretion from halo scales into the extended interstellar medium and toward the nucleus of a massive quasar host. The inflow rate implied by the combined emission and absorption constraints is well below levels required to sustain the quasar's radiative luminosity, suggesting anisotropic or variable accretion.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Dominika Wylezalek
Andrey Vayner
David S. N. Rupke
Nadia L. Zakamska
Sylvain Veilleux
Yuzo Ishikawa
Caroline Bertemes
Weizhe Liu
Jorge K. Barrera-Ballesteros
Hsiao-Wen Chen
Andy D. Goulding
Jenny E. Greene
Kevin N. Hainline
Nora Lützgendorf
Fred Hamann
Timothy Heckman
Sean D. Johnson
Dieter Lutz
Vincenzo Mainieri
Roberto Maiolino
摘要： Extremely red quasars, with bolometric luminosities exceeding $10^{47}$ erg s$^{-1}$, are a fascinating high-redshift population that is absent in the local universe. They are the best candidates for supermassive black holes accreting at rates at or above the Eddington limit, and they are associated with the most rapid and powerful outflows of ionized gas known to date. They are also hosted by massive galaxies. Here we present the first integral field unit (IFU) observations of a high-redshift quasar obtained by the Near Infrared Spectrograph (NIRSpec) on board the James Webb Space Telescope (JWST), which targeted SDSSJ165202.64+172852.3, an extremely red quasar at $z=2.94$. JWST observations reveal extended ionized gas - as traced by [OIII]$\lambda$5007\AA - in the host galaxy of the quasar, its outflow, and the circumgalactic medium. The complex morphology and kinematics imply that the quasar resides in a very dense environment with several interacting companion galaxies within projected distances of 10-15 kpc. The high density of the environment and the large velocities of the companion galaxies suggest that this system may represent the core of a forming cluster of galaxies. The system is a good candidate for a merger of two or more dark matter halos, each with a mass of a few $10^{13}$ M$_\odot$ and traces potentially one of the densest knots at $z\sim3$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Zhijie Qu
Hsiao-Wen Chen
Gwen C. Rudie
Fakhri S. Zahedy
Sean D. Johnson
Erin Boettcher
Sebastiano Cantalupo
Mandy C. Chen
Kathy L. Cooksey
David DePalma
Claude-André Faucher-Giguère
Michael Rauch
Joop Schaye
Robert A. Simcoe
摘要： This paper presents a systematic study of the photoionization and thermodynamic properties of the cool circumgalactic medium (CGM) as traced by rest-frame ultraviolet absorption lines around 26 galaxies at redshift $z\lesssim1$. The study utilizes both high-quality far-ultraviolet and optical spectra of background QSOs and deep galaxy redshift surveys to characterize the gas density, temperature, and pressure of individual absorbing components and to resolve their internal non-thermal motions. The derived gas density spans more than three decades, from $\log (n_{\rm H}/{\rm cm^{-3}}) \approx -4$ to $-1$, while the temperature of the gas is confined in a narrow range of $\log (T/{\rm K})\approx 4.3\pm 0.3$. In addition, a weak anti-correlation between gas density and temperature is observed, consistent with the expectation of the gas being in photoionization equilibrium. Furthermore, decomposing the observed line widths into thermal and non-thermal contributions reveals that more than 30% of the components at $z\lesssim 1$ exhibit line widths driven by non-thermal motions, in comparison to $<20$% found at $z\approx 2$-3. Attributing the observed non-thermal line widths to intra-clump turbulence, we find that massive quenched galaxies on average exhibit higher non-thermal broadening/turbulent energy in their CGM compared to star-forming galaxies at $z\lesssim 1$. Finally, strong absorption features from multiple ions covering a wide range of ionization energy (e.g., from Mg II to O IV) can be present simultaneously in a single absorption system with kinematically aligned component structure, but the inferred pressure in different phases may differ by a factor of $\approx 10$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ke Ma
Haibin Zhang
Zheng Cai
Yongming Liang
Nobunari Kashikawa
Mingyu Li
Yunjing Wu
Qiong Li
Xiaohui Fan
Sean D. Johnson
Masami Ouchi
摘要： Cosmic variance introduces significant uncertainties into galaxy number density properties when surveying the high-z Universe with a small volume, such uncertainties produce the field-to-field variance of galaxy number $\sigma_{g}$ in observational astronomy. This uncertainty significantly affects the Luminosity Functions (LF) measurement of Lya Emitters (LAEs). For most previous Lya LF studies, $\sigma_{g}$ is often adopted from predictions by cosmological simulations, but barely confirmed by observations. Measuring cosmic variance requires a huge sample over a large volume, exceeding the capabilities of most astronomical instruments. In this study, we demonstrate an observational approach for measuring the cosmic variance contribution for $z\approx2.2$ Lya LFs. The LAE candidates are observed using narrowband and broadband of the Subaru/Hyper Suprime-Cam (HSC), with 8 independent fields, making the total survey area $\simeq11.62$deg$^2$ and a comoving volume of $\simeq8.71\times10^6$Mpc$^3$. These eight fields are selected using the project of MAMMOTH. We report a best-fit Schechter function with parameters $\alpha=-1.75$ (fixed), $L_{Ly\alpha}^{*}=5.18_{-0.40}^{+0.43} \times 10^{42}$erg s$^{-1}$ and $\phi_{Lya}^{*}=4.87_{-0.55}^{+0.54}\times10^{-4}$Mpc$^{-3}$ for the overall Lya LFs. After clipping out the regions that can bias the cosmic variance measurements, we calculate $\sigma_{g}$, by sampling LAEs within multiple pointings assigned on the field image. We investigate the relation between $\sigma_{g}$ and survey volume $V$, and fit a simple power law: $\sigma_g=k\times(\frac{V_{\rm eff}}{10^5 {\rm Mpc}^3})^{\beta}$. We find best-fit values of $-1.209_{-0.106}^{+0.106}$ for $\beta$ and $0.986_{-0.100}^{+0.108}$ for k. We compare our measurements with predictions from simulations and find that the cosmic variance of LAEs might be larger than that of general star-forming galaxies.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Haibin Zhang
Zheng Cai
Mingyu Li
Yongming Liang
Nobunari Kashikawa
Ke Ma
Yunjing Wu
Qiong Li
Sean D. Johnson
Satoshi Kikuta
Masami Ouchi
Xiaohui Fan
摘要： We report the large scale structure and clustering analysis of Ly$\alpha$ emitters (LAEs) and Ly$\alpha$ blobs (LABs) at $z=2.2-2.3$. Using 3,341 LAEs, 117 LABs, and 58 bright (Ly$\alpha$ luminosity $L_{\rm Ly\alpha}>10^{43.4}$ erg s$^{-1}$) LABs at $z=2.2-2.3$ selected with Subaru/Hyper Suprime-Cam (HSC), we calculate the LAE overdensity to investigate the large scale structure at $z=2$. We show that 74% LABs and 78% bright LABs locate in overdense regions, which is consistent with the trend found by previous studies that LABs generally locate in overdense regions. We find that one of our 8 fields dubbed J1349 contains $39/117\approx33\%$ of our LABs and $22/58\approx38\%$ of our bright LABs. A unique and overdense $24'\times12'$ ($\approx 40\times20$ comoving Mpc$^2$) region in J1349 has 12 LABs (8 bright LABs). By comparing to SSA22 that is one of the most overdense LAB regions found by previous studies, we show that the J1349 overdense region contains $\geq 2$ times more bright LABs than the SSA22 overdense region. We calculate the angular correlation functions (ACFs) of LAEs and LABs in the unique J1349 field and fit the ACFs with a power-law function to measure the slopes. The slopes of LAEs and LABs are similar, while the bright LABs show a $\approx 2$ times larger slope suggesting that bright LABs are more clustered than faint LABs and LAEs. We show that the amplitudes of ACFs of LABs are higher than LAEs, which suggests that LABs have a $\approx 10$ times larger galaxy bias and field-to-field variance than LAEs. The strong field-to-field variance is consistent with the large differences of LAB numbers in our 8 fields.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ke Ma
Haibin Zhang
Zheng Cai
Yongming Liang
Nobunari Kashikawa
Mingyu Li
Yunjing Wu
Qiong Li
Xiaohui Fan
Sean D. Johnson
Masami Ouchi
摘要： Cosmic variance introduces significant uncertainties into galaxy number density properties when surveying the high-z Universe with a small volume, such uncertainties produce the field-to-field variance of galaxy number $\sigma_{g}$ in observational astronomy. This uncertainty significantly affects the Luminosity Functions (LF) measurement of Lya Emitters (LAEs). For most previous Lya LF studies, $\sigma_{g}$ is often adopted from predictions by cosmological simulations, but barely confirmed by observations. Measuring cosmic variance requires a huge sample over a large volume, exceeding the capabilities of most astronomical instruments. In this study, we demonstrate an observational approach for measuring the cosmic variance contribution for $z\approx2.2$ Lya LFs. The LAE candidates are observed using narrowband and broadband of the Subaru/Hyper Suprime-Cam (HSC), with 8 independent fields, making the total survey area $\simeq11.62$deg$^2$ and a comoving volume of $\simeq8.71\times10^6$Mpc$^3$. These eight fields are selected using the project of MAMMOTH. We report a best-fit Schechter function with parameters $\alpha=-1.75$ (fixed), $L_{Ly\alpha}^{*}=5.18_{-0.40}^{+0.43} \times 10^{42}$erg s$^{-1}$ and $\phi_{Lya}^{*}=4.87_{-0.55}^{+0.54}\times10^{-4}$Mpc$^{-3}$ for the overall Lya LFs. After clipping out the regions that can bias the cosmic variance measurements, we calculate $\sigma_{g}$, by sampling LAEs within multiple pointings assigned on the field image. We investigate the relation between $\sigma_{g}$ and survey volume $V$, and fit a simple power law: $\sigma_g=k\times(\frac{V_{\rm eff}}{10^5 {\rm Mpc}^3})^{\beta}$. We find best-fit values of $-1.209_{-0.106}^{+0.106}$ for $\beta$ and $0.986_{-0.100}^{+0.108}$ for k. We compare our measurements with predictions from simulations and find that the cosmic variance of LAEs might be larger than that of general star-forming galaxies.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Mandy C. Chen
Hsiao-Wen Chen
Michael Rauch
Zhijie Qu
Sean D. Johnson
Jennifer I-Hsiu Li
Joop Schaye
Gwen C. Rudie
Fakhri S. Zahedy
Erin Boettcher
Kathy L. Cooksey
Sebastiano Cantalupo
摘要： We present the first empirical constraints on the turbulent velocity field of the diffuse circumgalactic medium around four luminous QSOs at $z\!\approx\!0.5$--1.1. Spatially extended nebulae of $\approx\!50$--100 physical kpc in diameter centered on the QSOs are revealed in [OII]$\lambda\lambda\,3727,3729$ and/or [OIII]$\lambda\,5008$ emission lines in integral field spectroscopic observations obtained using MUSE on the VLT. We measure the second- and third-order velocity structure functions (VSFs) over a range of scales, from $\lesssim\!5$ kpc to $\approx\!20$--50 kpc, to quantify the turbulent energy transfer between different scales in these nebulae. While no constraints on the energy injection and dissipation scales can be obtained from the current data, we show that robust constraints on the power-law slope of the VSFs can be determined after accounting for the effects of atmospheric seeing, spatial smoothing, and large-scale bulk flows. Out of the four QSO nebulae studied, one exhibits VSFs in spectacular agreement with the Kolmogorov law, expected for isotropic, homogeneous, and incompressible turbulent flows. The other three fields exhibit a shallower decline in the VSFs from large to small scales. However, with a limited dynamic range in the spatial scales in seeing-limited data, no constraints can be obtained for the VSF slopes of these three nebulae. For the QSO nebula consistent with the Kolmogorov law, we determine a turbulence energy cascade rate of $\approx\!0.2$ cm$^{2}$ s$^{-3}$. We discuss the implication of the observed VSFs in the context of QSO feeding and feedback in the circumgalactic medium.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yuan Qi Ni
Dae-Sik Moon
Maria R. Drout
Abigail Polin
David J. Sand
Santiago GonzÁlez-GaitÁn
Sang Chul Kim
Youngdae Lee
Hong Soo Park
D. Andrew Howell
Peter E. Nugent
Anthony L. Piro
Peter J. Brown
LluÍs Galbany
Jamison Burke
Daichi Hiramatsu
Griffin Hosseinzadeh
Stefano Valenti
Niloufar Afsariardchi
Jennifer E. Andrews
摘要： SN~2018aoz is a Type Ia SN with a $B$-band plateau and excess emission in the infant-phase light curves $\lesssim$ 1 day after first light, evidencing an over-density of surface iron-peak elements as shown in our previous study. Here, we advance the constraints on the nature and origin of SN~2018aoz based on its evolution until the nebular phase. Near-peak spectroscopic features show the SN is intermediate between two subtypes of normal Type Ia: Core-Normal and Broad-Line. The excess emission could have contributions from the radioactive decay of surface iron-peak elements as well as ejecta interaction with either the binary companion or a small torus of circumstellar material. Nebular-phase limits on H$\alpha$ and He~I favour a white dwarf companion, consistent with the small companion size constrained by the low early SN luminosity, while the absence of [O~I] and He~I disfavours a violent merger of the progenitor. Of the two main explosion mechanisms proposed to explain the distribution of surface iron-peak elements in SN~2018aoz, the asymmetric Chandrasekhar-mass explosion is less consistent with the progenitor constraints and the observed blueshifts of nebular-phase [Fe~II] and [Ni~II]. The helium-shell double-detonation explosion is compatible with the observed lack of C spectral features, but current 1-D models are incompatible with the infant-phase excess emission, $B_{\rm max}-V_{\rm max}$ color, and absence of nebular-phase [Ca~II]. Although the explosion processes of SN~2018aoz still need to be more precisely understood, the same processes could produce a significant fraction of Type Ia SNe that appear normal after $\sim$ 1 day.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Haibin Zhang
Zheng Cai
Mingyu Li
Yongming Liang
Nobunari Kashikawa
Ke Ma
Yunjing Wu
Qiong Li
Sean D. Johnson
Satoshi Kikuta
Masami Ouchi
Xiaohui Fan
摘要： We report the large scale structure and clustering analysis of Ly$\alpha$ emitters (LAEs) and Ly$\alpha$ blobs (LABs) at $z=2.2-2.3$. Using 3,341 LAEs, 117 LABs, and 58 bright (Ly$\alpha$ luminosity $L_{\rm Ly\alpha}>10^{43.4}$ erg s$^{-1}$) LABs at $z=2.2-2.3$ selected with Subaru/Hyper Suprime-Cam (HSC), we calculate the LAE overdensity to investigate the large scale structure at $z=2$. We show that 74% LABs and 78% bright LABs locate in overdense regions, which is consistent with the trend found by previous studies that LABs generally locate in overdense regions. We find that one of our 8 fields dubbed J1349 contains $39/117\approx33\%$ of our LABs and $22/58\approx38\%$ of our bright LABs. A unique and overdense $24'\times12'$ ($\approx 40\times20$ comoving Mpc$^2$) region in J1349 has 12 LABs (8 bright LABs). By comparing to SSA22 that is one of the most overdense LAB regions found by previous studies, we show that the J1349 overdense region contains $\geq 2$ times more bright LABs than the SSA22 overdense region. We calculate the angular correlation functions (ACFs) of LAEs and LABs in the unique J1349 field and fit the ACFs with a power-law function to measure the slopes. The slopes of LAEs and LABs are similar, while the bright LABs show a $\approx 2$ times larger slope suggesting that bright LABs are more clustered than faint LABs and LAEs. We show that the amplitudes of ACFs of LABs are higher than LAEs, which suggests that LABs have a $\approx 10$ times larger galaxy bias and field-to-field variance than LAEs. The strong field-to-field variance is consistent with the large differences of LAB numbers in our 8 fields.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Haibin Zhang
Zheng Cai
Yongming Liang
Ke Ma
Nobunari Kashikawa
Mingyu Li
Yunjing Wu
Qiong Li
Sean D. Johnson
Masami Ouchi
Xiaohui Fan
摘要： In this paper, we present a Ly$\alpha$ halo extended to $\sim200$ kpc identified by stacking $\sim 3300$ Ly$\alpha$ emitters at $z=2.2-2.3$. We carry out imaging observations and data reduction with Subaru/Hyper Suprime-Cam (HSC). Our total survey area is $\sim12$ deg$^2$ and imaging depths are $25.5-27.0$ mag. Using the imaging data, we select 1,240 and 2,101 LAE candidates at $z=2.2$ and 2.3, respectively. We carry out spectroscopic observations of our LAE candidates and data reduction with Magellan/IMACS to estimate the contamination rate of our LAE candidates. We find that the contamination rate of our sample is low (8%). We stack our LAE candidates with a median stacking method to identify the Ly$\alpha$ halo at $z=2$. We show that the Ly$\alpha$ halo is extended to $\sim200$ kpc at a surface brightness level of $10^{-20}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$. Comparing to previous studies, our Ly$\alpha$ halo is more extended at radii of $\sim25-100$ kpc, which is not likely caused by the contamination in our sample but by different redshifts and fields instead. To investigate how central galaxies affect surrounding LAHs, we divide our LAEs into subsamples based on the Ly$\alpha$ luminosity ($L_{\rm Ly\alpha}$), rest-frame Ly$\alpha$ equivalent width (EW$_0$), and UV magnitude (M$_{\rm uv}$). We stack the subsamples and find that higher $L_{\rm Ly\alpha}$, lower EW$_0$, and brighter M$_{\rm uv}$ cause more extended halos. Our results suggest that more massive LAEs generally have more extended Ly$\alpha$ halos.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Haibin Zhang
Zheng Cai
Yongming Liang
Ke Ma
Nobunari Kashikawa
Mingyu Li
Yunjing Wu
Qiong Li
Sean D. Johnson
Masami Ouchi
Xiaohui Fan
摘要： In this paper, we present a Ly$\alpha$ halo extended to $\sim200$ kpc identified by stacking $\sim 3300$ Ly$\alpha$ emitters at $z=2.2-2.3$. We carry out imaging observations and data reduction with Subaru/Hyper Suprime-Cam (HSC). Our total survey area is $\sim12$ deg$^2$ and imaging depths are $25.5-27.0$ mag. Using the imaging data, we select 1,240 and 2,101 LAE candidates at $z=2.2$ and 2.3, respectively. We carry out spectroscopic observations of our LAE candidates and data reduction with Magellan/IMACS to estimate the contamination rate of our LAE candidates. We find that the contamination rate of our sample is low (8%). We stack our LAE candidates with a median stacking method to identify the Ly$\alpha$ halo at $z=2$. We show that the Ly$\alpha$ halo is extended to $\sim200$ kpc at a surface brightness level of $10^{-20}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$. Comparing to previous studies, our Ly$\alpha$ halo is more extended at radii of $\sim25-100$ kpc, which is not likely caused by the contamination in our sample but by different redshifts and fields instead. To investigate how central galaxies affect surrounding LAHs, we divide our LAEs into subsamples based on the Ly$\alpha$ luminosity ($L_{\rm Ly\alpha}$), rest-frame Ly$\alpha$ equivalent width (EW$_0$), and UV magnitude (M$_{\rm uv}$). We stack the subsamples and find that higher $L_{\rm Ly\alpha}$, lower EW$_0$, and brighter M$_{\rm uv}$ cause more extended halos. Our results suggest that more massive LAEs generally have more extended Ly$\alpha$ halos.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Xiaodi Yu
Jiang-Tao Li
Zhijie Qu
Ian U. Roederer
Joel N. Bregman
Xiaohui Fan
Taotao Fang
Sean D. Johnson
Feige Wang
Jinyi Yang
摘要： Outflows from super-massive black holes (SMBHs) play an important role in the co-evolution of themselves, their host galaxies, and the larger scale environments. Such outflows are often characterized by emission and absorption lines in various bands and in a wide velocity range blueshifted from the systematic redshift of the host quasar. In this paper, we report a strong broad line region (BLR) outflow from the z~4.7 quasar BR 1202-0725 based on the high-resolution optical spectrum taken with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph installed on the 6.5m Magellan/Clay telescope, obtained from the `Probing the He II re-Ionization ERa via Absorbing C IV Historical Yield' (HIERACHY) project. This rest-frame ultraviolet (UV) spectrum is characterized by a few significantly blueshifted broad emission lines from high ions; the most significant one is the C IV line at a velocity of -6500 km/s relative to the H{\alpha} emission line, which is among the highest velocity BLR outflows in observed quasars at z > 4. The measured properties of UV emission lines from different ions, except for O I and Ly{\alpha}, also follow a clear trend that higher ions tend to be broader and outflow at higher average velocities. There are multiple C IV and Si IV absorbing components identified on the blue wings of the corresponding emission lines, which may be produced by either the outflow or the intervening absorbers.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yuan Qi Ni
Dae-Sik Moon
Maria R. Drout
Abigail Polin
David J. Sand
Santiago Gonzalez-Gaitan
Sang Chul Kim
Youngdae Lee
Hong Soo Park
D. Andrew Howell
Peter E. Nugent
Anthony L. Piro
Peter J. Brown
Lluis Galbany
Jamison Burke
Daichi Hiramatsu
Griffin Hosseinzadeh
Stefano Valenti
Niloufar Afsariardchi
Jennifer E. Andrews
摘要： Type Ia Supernovae are thermonuclear explosions of white dwarf stars. They play a central role in the chemical evolution of the Universe and are an important measure of cosmological distances. However, outstanding questions remain about their origins. Despite extensive efforts to obtain natal information from their earliest signals, observations have thus far failed to identify how the majority of them explode. Here, we present infant-phase detections of SN 2018aoz from a brightness of -10.5 absolute AB magnitudes -- the lowest luminosity early Type Ia signals ever detected -- revealing a hitherto unseen plateau in the $B$-band that results in a rapid redward color evolution between 1.0 and 12.4 hours after the estimated epoch of first light. The missing $B$-band flux is best-explained by line-blanket absorption from Fe-peak elements in the outer 1% of the ejected mass. The observed $B-V$ color evolution of the SN also matches the prediction from an over-density of Fe-peak elements in the same outer 1% of the ejected mass, whereas bluer colors are expected from a purely monotonic distribution of Fe-peak elements. The presence of excess nucleosynthetic material in the extreme outer layers of the ejecta points to enhanced surface nuclear burning or extended sub-sonic mixing processes in some normal Type Ia Supernova explosions.
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