Decreasing and reading output of a sensor (0 - 10 V) using a voltage divider - Output impedance
Looking at the datasheet, it does look like it needs a load resistance of more than 10kOhm. 

The total load resistance of your potential divider will depend on two things: the value of your resistors, and the input resistance of whatever you're connecting to the divider output.

Since you're connecting the divider output directly to the arduino ADC, and the ADC input resistance is very high, the only thing you really have to worry about is the resistor value.

The total resistance of your divider will therefore just be R1+R2, so you need to make sure that this adds up to >10kOhm. I would make the total resistance >20kOhm just in case.