标题： 追踪人马座矮星系的外部结构：在10到34度角距离处的探测 显示英文标题

标题： Tracing the Outer Structure of the Sagittarius Dwarf Galaxy: Detections at Angular Distances Between 10 and 34 Degrees

摘要： 我们获得了在人马座矮椭球星系（Sgr dSph）主轴东南延伸方向的24个区域以及西北延伸方向的4个区域内的深光度数据。利用色星图中预期的人马座上主序星位置的恒星计数，我们在距离银河系中心10到34度的范围内明确检测到了东南方向的人马座恒星。如果人马座是对称的，这表明其真实主轴直径至少为68度，或者将近30千秒差距，假设人马座的所有部分与太阳的距离相等。平行于星系短轴的恒星计数显示，即使远离其核心，人马座仍然相当宽广。这表明人马座外部区域更像一条流，而非椭球形内核区域的延伸。推断出的V波段表面亮度（SB）轮廓在此半径范围内从每平方角秒27.3到30.5星等变化，并且在距离人马座中心约20度处显示出坡度的变化。外层表面亮度轮廓的尺度长度为17.2度，而人马座核心区域的尺度长度为4.7度。我们推测此表面亮度轮廓的转折点代表了从人马座主体到更广泛‘人马座流’的过渡。通过整合表面亮度轮廓，我们估计人马座的绝对视星等范围为-13.4到-14.6，具体取决于人马座的结构假设；因此，人马座的发光上限约为5.8×10⁷太阳光度。这一结果降低了Ibata等人（1997年）推断出的人马座V波段M/L比值至约10，与银河系最亮dSph伴星所观测到的值一致。 显示英文摘要

摘要： We have obtained deep photometric data in 24 fields along the southeast extension of the major axis of the Sagittarius dwarf spheroidal (Sgr dSph) galaxy, and in four fields along the northwest extension. Using star counts at the expected position of the Sgr upper main-sequence within the resulting color-magnitude diagrams (CMDs), we unambiguously detect Sgr stars in the southeast over the range 10--34 degreesfrom the galaxy's center. If Sgr is symmetric, this implies a true major-axis diameter of at least 68 degrees, or nearly 30 kpc if all portions of Sgr are equally distant from the Sun. Star counts parallel to the galaxy's minor-axis reveal that Sgr remains quite broad far from its center. This suggests that the outer portions of Sgr resemble a stream rather than an extension of the ellipsoidal inner regions of the galaxy. The inferred V-band surface brightness (SB) profile ranges from 27.3-30.5 mag per arcsec**2 over this radial range and exhibits a change in slope approx 20 degrees from the center of Sgr. The scale length of the outer SB profile is 17.2 degrees, compared to 4.7 degrees in the central region of Sgr. We speculate that this break in the SB profile represents a transition from the main body of Sgr to a more extended `Sgr stream'. By integrating the SB profile we estimate that the absolute visual magnitude of Sgr lies in the range -13.4 to -14.6, depending on the assumed structure of Sgr; an upper limit to the luminosity of Sgr is therefore approx 5.8x10**7 Solar Luminosities. This result lowers the V-band M/L ratio inferred for Sgr by Ibata et al. (1997) down to approx 10, consistent with values observed in the most luminous dSph companions of the Milky Way.