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首页> 外文期刊>The Astrophysical journal >LOW SURFACE BRIGHTNESS Ha OBSERVATIONS OF LOCAL INTERGALACTIC HYDROGEN CLOUDS
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LOW SURFACE BRIGHTNESS Ha OBSERVATIONS OF LOCAL INTERGALACTIC HYDROGEN CLOUDS

机译：低表面亮度Ha观察到的局部星际氢云团

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摘要

We present upper limits on the local ionizing background based on a search for extended Ha emission from three nearby intergalactic H I clouds: the Leo Ring (M96 group), both the NE and SW lobes of the Haynes-Giovanelli Virgo Cloud (H I 1225+01), and the H I tidal tails associated with the NGC 4631/4656 group. These clouds were chosen to have 21 cm emission that is extended (10-100 kpc) and distant from any associated galaxy. Deep, wide-field CCD images were acquired through narrow- (～31 A) and broadband R filters with the Burrell Schmidt telescope on Kitt Peak. We set a 95% confidence upper limit on the Hα surface brightness for the areas of the clouds detected in H I of 1.6 x 10~(-19) ergs s~(-1) cm~(-2) arcsec~(-2) in Leo and of 3.7 x 10~(-19) ergs s~(-1) cm~(-2) arcsec~(-2) in Virgo. We limit the local ionizing background to Φ_0 < 5.0 x 10~3 photons s~(-1) cm~(-2) sr~(-1) (95%) at the location of the Leo Ring cloud and Φ_0 < 1.1 x 10~4 photons s~(-1) cm~(-2) sr~(-1) at the Virgo cloud, assuming spherical clouds. (Limits are a factor of 2 higher for a thin face-on slab.) The limits correspond to J_0 < 3.3 x 10~(-23) and 7.6 x 10~(-23) ergs s~(-1) cm~(-2) sr~(-1) Hz~(-1) for a v~(-1/2) spectrum (1.6 times higher for a v~(-1.4) spectrum) between 1 and 4 ryd. Such low limits suggest that quasar light, and not galactic light, dominates the ionizing background at low redshift. The Hα limit on the Leo cloud is significantly below a previously reported detection. In the field of the edge-on galaxies NGC 4631 and NGC 4656, we detect Hα from ionized gas extending nearly 16 kpc above N4631, which could have been blown out by starburst activity in the plane, and a low surface brightness companion or stellar tidal tail. This companion lies between N4631's H I tidal tails and may have played a role in creating the H I tidal tails, or it may represent star formation within the tidal tails. We also report the tentative detection of an ultrafaint "sheet" of Hα emission extending from NGC 4631 to NGC 4656.
机译：我们基于对附近三个银河系HI云的扩展Ha发射的搜索来提出局部电离背景的上限：狮子座环（M96组），海恩斯-乔万内利处女座云的NE和SW瓣（HI 1225 + 01 ），以及与NGC 4631/4656组相关的HI潮汐尾。这些云被选择具有21 cm的发射范围，该发射范围是扩展的（10-100 kpc），并且远离任何关联的星系。在基特峰的Burrell Schmidt望远镜通过狭窄的（〜31 A）和宽带R滤光片获得了深广域CCD图像。对于在HI中检测到的云区域，我们将Hα表面亮度的95％置信上限设置为1.6 x 10〜（-19）ergs s〜（-1）cm〜（-2）arcsec〜（-2）在狮子座中为3.7 x 10〜（-19）ergs s〜（-1）cm〜（-2）arcsec〜（-2）在处女座。我们将局部电离背景限制在狮子环云的位置和Φ_0<1.1 x处的Φ_0<5.0 x 10〜3个光子s〜（-1）cm〜（-2）sr〜（-1）（95％）在处女座云上有10〜4个光子s〜（-1）cm〜（-2）sr〜（-1），假设是球形云。 （对于薄的面板，极限值要高2倍。）该极限值对应于J_0 <3.3 x 10〜（-23）和7.6 x 10〜（-23）ers s〜（-1）cm〜（ av〜（-1/2）光谱为-2）sr〜（-1）Hz〜（-1）（av〜（-1.4）光谱为sr〜（-1）Hz的1.6倍）。如此低的限制表明类星体光而非银河系光在低红移下主导着电离背景。狮子座云的Hα极限显着低于先前报告的检测。在边缘星系NGC 4631和NGC 4656的领域中，我们从电离气体中检测到了Hα，该气体在N4631上方延伸了近16 kpc，这可能是由于飞机中的星暴活动所吹走的，并且表面亮度低伴星或恒星潮汐尾巴。该伴星位于N4631的H I潮汐尾之间，并且可能在创建H I潮汐尾中起到了作用，或者它可能代表潮汐尾内的恒星形成。我们还报告了从NGC 4631到NGC 4656的Hα发射超微弱“薄片”的初步检测。

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