اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدExtended Lyman-Alpha Emission around Star-forming Galaxies
161
0
0.0
(
0
)
تأليف
Zheng Zheng
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Lyman-alpha (Lya) photons that escape the interstellar medium of star-forming galaxies may be resonantly scattered by neutral hydrogen atoms in the circumgalactic and intergalactic media, thereby increasing the angular extent of the galaxys Lya emission. We present predictions of this extended, low surface brightness Lya emission based on radiative transfer modeling in a cosmological reionization simulation. The extended emission can be detected from stacked narrowband images of Lya emitters (LAEs) or of Lyman break galaxies (LBGs). Its average surface brightness profile has a central cusp, then flattens to an approximate plateau beginning at an inner characteristic scale below ~0.2 Mpc (comoving), then steepens again beyond an outer characteristic scale of ~1 Mpc. The inner scale marks the transition from scattered light of the central source to emission from clustered sources, while the outer scale marks the spatial extent of scattered emission from these clustered sources. Both scales tend to increase with halo mass, UV luminosity, and observed Lya luminosity. The extended emission predicted by our simulation is already within reach of deep narrowband photometry using large ground-based telescopes. Such observations would test radiative transfer models of emission from LAEs and LBGs, and they would open a new window on the circumgalactic environment of high-redshift star-forming galaxies.
قيم البحث
اقرأ أيضاً
We report the detection of extended Lyman-alpha (Lya) haloes around 145 individual star-forming galaxies at redshifts 3<z<6 in the Hubble Ultra Deep Field observed with the Multi-Unit Spectroscopic Explorer at ESO-VLT. Our sample consists of continuu
m-faint (-15> M_{UV}> -22) Lya emitters (LAEs). Using a 2D, two-component decomposition of Lya emission assuming circular exponential distributions, we measure scale lengths and luminosities of Lya haloes. We find that 80% of our objects having reliable Lya halo measurements show Lya emission that is significantly more extended than the UV continuum detected by HST (by a factor ~4 to >20). The median exponential scale length of the Lya haloes in our sample is ~4.5 kpc. By comparing the maximal detected extent of the Lya emission with the predicted dark matter halo virial radii of simulated galaxies, we show that the detected Lya emission of our selected sample of LAEs probes a significant portion of the cold circum-galactic medium (CGM) of these galaxies (>50% in average). This result shows that there must be significant HI reservoirs in the CGM and reinforces the idea that Lya haloes are ubiquitous around high-redshift Lya emitting galaxies. Our characterization of the Lya haloes indicates that the majority of the Lya flux comes from the halo (~65%) and that their scale lengths seem to be linked to the UV properties of the galaxies. We do not observe a significant Lya halo size evolution with redshift. We also find that the Lya lines cover a large range of full width at half maximum (FWHM) from 118 to 512 km/s. While the FWHM does not seem to be correlated to the Lya scale length, most compact Lya haloes and those that are not detected with high significance tend to have narrower Lya profiles. Finally, we investigate the origin of the extended Lya emission but we conclude that our data do not allow us to disentangle the possible processes.
We discuss new Keck/MOSFIRE spectroscopic observations of four luminous galaxies at z~7-9 selected to have intense optical line emission by Roberts-Borsani et al. (2016). Previous follow-up has revealed Lyman-alpha in two of the four galaxies. Our ne
w MOSFIRE observations confirm that Lyman-alpha is present in the entire sample. We detect Lyman-alpha emission in COS-zs7-1, confirming its redshift as z=7.154, and we detect Lyman-alpha in EGS-zs8-2 at z=7.477, verifying a tentative detection presented in an earlier study. The ubiquity of Lyman-alpha in this sample is puzzling given that the IGM is likely significantly neutral over 7<z<9. To investigate this result in more detail, we have initiated a campaign to target UV metal emission in the four Lyman-alpha emitters as a probe of both the radiation field and the velocity offset of Lyman-alpha. Here we present the detection of intense CIII] emission in EGS-zs8-1, a galaxy from this sample previously shown to have Lyman-alpha at z=7.73. Photoionization models indicate that an intense radiation field and low metallicity are required to reproduce the intense CIII] and optical line emission. We argue that this extreme radiation field is likely to affect the local environment, increasing the transmission of Lyman-alpha through the galaxy. Moreover, the centroid of CIII] indicates that Lyman-alpha is redshifted from the systemic value by 340 km/s. This velocity offset is larger than that seen in less luminous systems, providing an additional explanation for the transmission of Lyman-alpha emission through the IGM. Since the transmission is further enhanced by the likelihood that such systems are also situated in the densest regions with the largest ionized bubbles, the visibility of Lyman-alpha at z>7 is expected to be strongly luminosity-dependent, with the most effective transmission occurring in systems with intense star formation.
Ly$alpha$ photons scattered by neutral hydrogen atoms in the circumgalactic media or produced in the halos of star-forming galaxies are expected to lead to extended Ly$alpha$ emission around galaxies. Such low surface brightness Ly$alpha$ halos (LAHs
) have been detected by stacking Ly$alpha$ images of high-redshift star-forming galaxies. We study the origin of LAHs by performing radiative transfer modeling of nine $z=3.1$ Lyman-Alpha Emitters (LAEs) in a high resolution hydrodynamic cosmological galaxy formation simulation. We develop a method of computing the mean Ly$alpha$ surface brightness profile of each LAE by effectively integrating over many different observing directions. Without adjusting any parameters, our model yields an average Ly$alpha$ surface brightness profile in remarkable agreement with observations. We find that observed LAHs cannot be accounted for solely by photons originating from the central LAE and scattered to large radii by hydrogen atoms in the circumgalactic gas. Instead, Ly$alpha$ emission from regions in the outer halo is primarily responsible for producing the extended LAHs seen in observations, which potentially includes both star-forming and cooling radiation. With the limit on the star formation contribution set by the ultra-violet (UV) halo measurement, we find that cooling radiation can play an important role in forming the extended LAHs. We discuss the implications and caveats of such a picture.
A large number of high-redshift galaxies have been discovered via their narrow-band Lya line or broad-band continuum colors in recent years. The nature of the escaping process of photons from these early galaxies is crucial to understanding galaxy ev
olution and the cosmic reionization. Here, we investigate the escape of Lya, non-ionizing UV-continuum (l = 1300 - 1600 angstrom in rest frame), and ionizing photons (l < 912 angstrom) from galaxies by combining a cosmological hydrodynamic simulation with three-dimensional multi-wavelength radiative transfer calculations. The galaxies are simulated in a box of 5^3 h^-3 Mpc^3 with high resolutions using the Aquila initial condition which reproduces a Milky Way-like galaxy at redshift z=0. We find that the escape fraction (fesc) of these different photons shows a complex dependence on redshift and galaxy properties: fesc(Lya) and fesc(UV) appear to evolve with redshift, and they show similar, weak correlations with galaxy properties such as mass, star formation, metallicity, and dust content, while fesc(Ion) remains roughly constant at ~ 0.2 from z ~ 0 - 10, and it does not show clear dependence on galaxy properties. fesc(Lya) correlates more strongly with fesc(UV) than with fesc(Ion). In addition, we find a relation between the emergent Lya luminosity and the ionizing photon emissivity of Lyman Alpha Emitters (LAEs). By combining this relation with the observed luminosity functions of LAEs at different redshift, we estimate the contribution from LAEs to the reionization of intergalactic medium (IGM). Our result suggests that ionizing photons from LAEs alone are not sufficient to ionize IGM at z > 6, but they can maintain the ionization of IGM at z ~ 0 - 5.
{Abridged} We investigate the observability of cold accretion streams at redshift 3 via Lyman-alpha (Lya) emission and the feasibility of cold accretion as the main driver of Lya blobs (LABs). We run cosmological zoom simulations focusing on 3 halos
spanning two orders of magnitude in mass, roughly from 10^11 to 10^13 solar masses. We use a version of the Ramses code that includes radiative transfer of UV photons, and we employ a refinement strategy that allows us to resolve accretion streams in their natural environment to an unprecedented level. For the first time, we self-consistently model self-shielding in the cold streams from the cosmological UV background, which enables us to predict their temperatures, ionization states and Lya luminosities with improved accuracy. We find the efficiency of gravitational heating in cold streams in a ~10^11 solar mass halo is around 10-20% throughout most of the halo but reaching much higher values close to the center. As a result most of the Lya luminosity comes from gas which is concentrated at the central 20% of the halo radius, leading to Lya emission which is not extended. In more massive halos, of >10^12 solar masses, cold accretion is complex and disrupted, and gravitational heating does not happen as a steady process. Ignoring the factors of Lya scattering, local UV enhancement, and SNe feedback, cold accretion alone in these massive halos can produce LABs that largely agree with observations in terms of morphology, extent, and luminosity. Our simulations slightly and systematically over-predict LAB abundances, perhaps hinting that the interplay of these ignored factors may have a negative net effect on extent and luminosity. We predict that a factor of a few increase in sensitivity from current observational limits should unambiguously reveal continuum-free accretion streams around massive galaxies at z=3.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
